diff --git a/core/src/avm2/globals/string.rs b/core/src/avm2/globals/string.rs
index d0bddb788..241ce1513 100644
--- a/core/src/avm2/globals/string.rs
+++ b/core/src/avm2/globals/string.rs
@@ -497,6 +497,46 @@ fn substring<'gc>(
     Ok(Value::Undefined)
 }
 
+/// Implements `String.toLowerCase`
+fn to_lower_case<'gc>(
+    activation: &mut Activation<'_, 'gc, '_>,
+    this: Option<Object<'gc>>,
+    _args: &[Value<'gc>],
+) -> Result<Value<'gc>, Error> {
+    if let Some(this) = this {
+        let this_val = Value::from(this);
+        let this = this_val.coerce_to_string(activation)?;
+        return Ok(AvmString::new(
+            activation.context.gc_context,
+            this.iter()
+                .map(crate::string::utils::swf_to_lowercase)
+                .collect::<WString>(),
+        )
+        .into());
+    }
+    Ok(Value::Undefined)
+}
+
+/// Implements `String.toUpperCase`
+fn to_upper_case<'gc>(
+    activation: &mut Activation<'_, 'gc, '_>,
+    this: Option<Object<'gc>>,
+    _args: &[Value<'gc>],
+) -> Result<Value<'gc>, Error> {
+    if let Some(this) = this {
+        let this_val = Value::from(this);
+        let this = this_val.coerce_to_string(activation)?;
+        return Ok(AvmString::new(
+            activation.context.gc_context,
+            this.iter()
+                .map(crate::string::utils::swf_to_uppercase)
+                .collect::<WString>(),
+        )
+        .into());
+    }
+    Ok(Value::Undefined)
+}
+
 /// Construct `String`'s class.
 pub fn create_class<'gc>(mc: MutationContext<'gc, '_>) -> GcCell<'gc, Class<'gc>> {
     let class = Class::new(
@@ -530,6 +570,8 @@ pub fn create_class<'gc>(mc: MutationContext<'gc, '_>) -> GcCell<'gc, Class<'gc>
         ("split", split),
         ("substr", substr),
         ("substring", substring),
+        ("toLowerCase", to_lower_case),
+        ("toUpperCase", to_upper_case),
     ];
     write.define_as3_builtin_instance_methods(mc, AS3_INSTANCE_METHODS);
 
diff --git a/tests/tests/regression_tests.rs b/tests/tests/regression_tests.rs
index 9bbe733e5..d45b8849a 100644
--- a/tests/tests/regression_tests.rs
+++ b/tests/tests/regression_tests.rs
@@ -483,6 +483,7 @@ swf_tests! {
     (as3_stage_properties, "avm2/stage_properties", 1),
     (as3_stored_properties, "avm2/stored_properties", 1),
     (as3_strict_equality, "avm2/strict_equality", 1),
+    (as3_string_case, "avm2/string_case", 1),
     (as3_string_char_at, "avm2/string_char_at", 1),
     (as3_string_char_code_at, "avm2/string_char_code_at", 1),
     (as3_string_concat_fromcharcode, "avm2/string_concat_fromcharcode", 1),
diff --git a/tests/tests/swfs/avm2/string_case/Test.as b/tests/tests/swfs/avm2/string_case/Test.as
new file mode 100644
index 000000000..2288df517
--- /dev/null
+++ b/tests/tests/swfs/avm2/string_case/Test.as
@@ -0,0 +1,23 @@
+package {
+	public class Test {
+		public function Test() {}
+	}
+}
+
+// toLowerCase
+trace("// toLowerCase");
+
+trace('// "teST😋".toLowerCase()');
+trace("teST😋".toLowerCase());
+trace('// All uppercase chars');
+trace("ABCDEFGHIJKLMNOPQRSTUVWXYZÀÁÂÃÄÅÆÇÈÉÊËÌÍÎÏÐÑÒÓÔÕÖØÙÚÛÜÝÞĀĂĄĆĈĊČĎĐĒĔĖĘĚĜĞĠĢĤĦĨĪĬĮİIJĴĶĹĻĽĿŁŃŅŇŊŌŎŐŒŔŖŘŚŜŞŠŢŤŦŨŪŬŮŰŲŴŶŸŹŻŽƁƂƄƆƇƉƊƋƎƏƐƑƓƔƖƗƘƜƝƟƠƢƤƦƧƩƬƮƯƱƲƳƵƷƸƼDŽDžLJLjNJNjǍǏǑǓǕǗǙǛǞǠǢǤǦǨǪǬǮDZDzǴǶǷǸǺǼǾȀȂȄȆȈȊȌȎȐȒȔȖȘȚȜȞȢȤȦȨȪȬȮȰȲΆΈΉΊΌΎΏΑΒΓΔΕΖΗΘΙΚΛΜΝΞΟΠΡ΢ΣΤΥΦΧΨΩΪΫϘϚϜϞϠϢϤϦϨϪϬϮϴЀЁЂЃЄЅІЇЈЉЊЋЌЍЎЏАБВГДЕЖЗИЙКЛМНОПРСТУФХЦЧШЩЪЫЬЭЮЯѠѢѤѦѨѪѬѮѰѲѴѶѸѺѼѾҀҊҌҎҐҒҔҖҘҚҜҞҠҢҤҦҨҪҬҮҰҲҴҶҸҺҼҾӁӃӇӋӐӒӔӖӘӚӜӞӠӢӤӦӨӪӬӮӰӲӴӶӸԱԲԳԴԵԶԷԸԹԺԻԼԽԾԿՀՁՂՃՄՅՆՇՈՉՊՋՌՍՎՏՐՑՒՓՔՕՖႠႡႢႣႤႥႦႧႨႩႪႫႬႭႮႯႰႱႲႳႴႵႶႷႸႹႺႻႼႽႾႿჀჁჂჃჄჅḀḂḄḆḈḊḌḎḐḒḔḖḘḚḜḞḠḢḤḦḨḪḬḮḰḲḴḶḸḺḼḾṀṂṄṆṈṊṌṎṐṒṔṖṘṚṜṞṠṢṤṦṨṪṬṮṰṲṴṶṸṺṼṾẀẂẄẆẈẊẌẎẐẒẔẠẢẤẦẨẪẬẮẰẲẴẶẸẺẼẾỀỂỄỆỈỊỌỎỐỒỔỖỘỚỜỞỠỢỤỦỨỪỬỮỰỲỴỶỸἈἉἊἋἌἍἎἏἘἙἚἛἜἝἨἩἪἫἬἭἮἯἸἹἺἻἼἽἾἿὈὉὊὋὌὍὙὛὝὟὨὩὪὫὬὭὮὯᾈᾉᾊᾋᾌᾍᾎᾏᾘᾙᾚᾛᾜᾝᾞᾟᾨᾩᾪᾫᾬᾭᾮᾯᾸᾹᾺΆᾼῈΈῊΉῌῘῙῚΊῨῩῪΎῬῸΌῺΏῼΩKÅⅠⅡⅢⅣⅤⅥⅦⅧⅨⅩⅪⅫⅬⅭⅮⅯⒶⒷⒸⒹⒺⒻⒼⒽⒾⒿⓀⓁⓂⓃⓄⓅⓆⓇⓈⓉⓊⓋⓌⓍⓎⓏＡＢＣＤＥＦＧＨＩＪＫＬＭＮＯＰＱＲＳＴＵＶＷＸＹＺ".toLowerCase());
+trace("");
+
+// toUpperCase
+trace("// toUpperCase");
+trace('// "teST😋".toUpperCase()');
+trace("teST😋".toUpperCase());
+trace('// All lowercase chars');
+var s = "abcdefghijklmnopqrstuvwxyzàáâãäåæçèéêëìíîïðñòóôõöøùúûüýþÿāăąćĉċčďđēĕėęěĝğġģĥħĩīĭįıijĵķĺļľŀłńņňŋōŏőœŕŗřśŝşšţťŧũūŭůűųŵŷźżžſƃƅƈƌƒƕƙơƣƥƨƭưƴƶƹƽƿDždžLjljNjnjǎǐǒǔǖǘǚǜǝǟǡǣǥǧǩǫǭǯDzdzǵǹǻǽǿȁȃȅȇȉȋȍȏȑȓȕȗșțȝȟȣȥȧȩȫȭȯȱȳɓɔɖɗəɛɠɣɨɩɯɲɵʀʃʈʊʋʒͅάέήίαβγδεζηθικλμνξοπρςστυφχψωϊϋόύώϐϑϕϖϙϛϝϟϡϣϥϧϩϫϭϯϰϱϲϵабвгдежзийклмнопрстуфхцчшщъыьэюяѐёђѓєѕіїјљњћќѝўџѡѣѥѧѩѫѭѯѱѳѵѷѹѻѽѿҁҋҍҏґғҕҗҙқҝҟҡңҥҧҩҫҭүұҳҵҷҹһҽҿӂӄӈӌӑӓӕӗәӛӝӟӡӣӥӧөӫӭӯӱӳӵӷӹաբգդեզէըթժիլխծկհձղճմյնշոչպջռսվտրցւփքօֆḁḃḅḇḉḋḍḏḑḓḕḗḙḛḝḟḡḣḥḧḩḫḭḯḱḳḵḷḹḻḽḿṁṃṅṇṉṋṍṏṑṓṕṗṙṛṝṟṡṣṥṧṩṫṭṯṱṳṵṷṹṻṽṿẁẃẅẇẉẋẍẏẑẓẕẛạảấầẩẫậắằẳẵặẹẻẽếềểễệỉịọỏốồổỗộớờởỡợụủứừửữựỳỵỷỹἀἁἂἃἄἅἆἇἐἑἒἓἔἕἠἡἢἣἤἥἦἧἰἱἲἳἴἵἶἷὀὁὂὃὄὅὑὓὕὗὠὡὢὣὤὥὦὧὰάὲέὴήὶίὸόὺύὼώᾀᾁᾂᾃᾄᾅᾆᾇᾐᾑᾒᾓᾔᾕᾖᾗᾠᾡᾢᾣᾤᾥᾦᾧᾰᾱᾳιῃῐῑῠῡῥῳⅰⅱⅲⅳⅴⅵⅶⅷⅸⅹⅺⅻⅼⅽⅾⅿⓐⓑⓒⓓⓔⓕⓖⓗⓘⓙⓚⓛⓜⓝⓞⓟⓠⓡⓢⓣⓤⓥⓦⓧⓨⓩａｂｃｄｅｆｇｈｉｊｋｌｍｎｏｐｑｒｓｔｕｖｗｘｙｚ";
+trace(s.toUpperCase());
+trace("");
\ No newline at end of file
diff --git a/tests/tests/swfs/avm2/string_case/output.txt b/tests/tests/swfs/avm2/string_case/output.txt
new file mode 100644
index 000000000..580a60454
--- /dev/null
+++ b/tests/tests/swfs/avm2/string_case/output.txt
@@ -0,0 +1,12 @@
+// toLowerCase
+// "teST😋".toLowerCase()
+test😋
+// All uppercase chars
+abcdefghijklmnopqrstuvwxyzàáâãäåæçèéêëìíîïðñòóôõöøùúûüýþāăąćĉċčďđēĕėęěĝğġģĥħĩīĭįiijĵķĺļľŀłńņňŋōŏőœŕŗřśŝşšţťŧũūŭůűųŵŷÿźżžɓƃƅɔƈɖɗƌǝəɛƒɠɣɩɨƙɯɲɵơƣƥʀƨʃƭʈưʊʋƴƶʒƹƽdždžljljnjnjǎǐǒǔǖǘǚǜǟǡǣǥǧǩǫǭǯdzdzǵƕƿǹǻǽǿȁȃȅȇȉȋȍȏȑȓȕȗșțȝȟȣȥȧȩȫȭȯȱȳάέήίόύώαβγδεζηθικλμνξοπρςστυφχψωϊϋϙϛϝϟϡϣϥϧϩϫϭϯθѐёђѓєѕіїјљњћќѝўџабвгдежзийклмнопрстуфхцчшщъыьэюяѡѣѥѧѩѫѭѯѱѳѵѷѹѻѽѿҁҋҍҏґғҕҗҙқҝҟҡңҥҧҩҫҭүұҳҵҷҹһҽҿӂӄӈӌӑӓӕӗәӛӝӟӡӣӥӧөӫӭӯӱӳӵӷӹաբգդեզէըթժիլխծկհձղճմյնշոչպջռսվտրցւփքօֆაბგდევზთიკლმნოპჟრსტუფქღყშჩცძწჭხჯჰჱჲჳჴჵḁḃḅḇḉḋḍḏḑḓḕḗḙḛḝḟḡḣḥḧḩḫḭḯḱḳḵḷḹḻḽḿṁṃṅṇṉṋṍṏṑṓṕṗṙṛṝṟṡṣṥṧṩṫṭṯṱṳṵṷṹṻṽṿẁẃẅẇẉẋẍẏẑẓẕạảấầẩẫậắằẳẵặẹẻẽếềểễệỉịọỏốồổỗộớờởỡợụủứừửữựỳỵỷỹἀἁἂἃἄἅἆἇἐἑἒἓἔἕἠἡἢἣἤἥἦἧἰἱἲἳἴἵἶἷὀὁὂὃὄὅὑὓὕὗὠὡὢὣὤὥὦὧᾀᾁᾂᾃᾄᾅᾆᾇᾐᾑᾒᾓᾔᾕᾖᾗᾠᾡᾢᾣᾤᾥᾦᾧᾰᾱὰάᾳὲέὴήῃῐῑὶίῠῡὺύῥὸόὼώῳωkåⅰⅱⅲⅳⅴⅵⅶⅷⅸⅹⅺⅻⅼⅽⅾⅿⓐⓑⓒⓓⓔⓕⓖⓗⓘⓙⓚⓛⓜⓝⓞⓟⓠⓡⓢⓣⓤⓥⓦⓧⓨⓩａｂｃｄｅｆｇｈｉｊｋｌｍｎｏｐｑｒｓｔｕｖｗｘｙｚ
+
+// toUpperCase
+// "teST😋".toUpperCase()
+TEST😋
+// All lowercase chars
+ABCDEFGHIJKLMNOPQRSTUVWXYZÀÁÂÃÄÅÆÇÈÉÊËÌÍÎÏÐÑÒÓÔÕÖØÙÚÛÜÝÞŸĀĂĄĆĈĊČĎĐĒĔĖĘĚĜĞĠĢĤĦĨĪĬĮIIJĴĶĹĻĽĿŁŃŅŇŊŌŎŐŒŔŖŘŚŜŞŠŢŤŦŨŪŬŮŰŲŴŶŹŻŽSƂƄƇƋƑǶƘƠƢƤƧƬƯƳƵƸƼǷDŽDŽLJLJNJNJǍǏǑǓǕǗǙǛƎǞǠǢǤǦǨǪǬǮDZDZǴǸǺǼǾȀȂȄȆȈȊȌȎȐȒȔȖȘȚȜȞȢȤȦȨȪȬȮȰȲƁƆƉƊƏƐƓƔƗƖƜƝƟƦƩƮƱƲƷΙΆΈΉΊΑΒΓΔΕΖΗΘΙΚΛΜΝΞΟΠΡ΢ΣΤΥΦΧΨΩΪΫΌΎΏΒΘΦΠϘϚϜϞϠϢϤϦϨϪϬϮΚΡΣΕАБВГДЕЖЗИЙКЛМНОПРСТУФХЦЧШЩЪЫЬЭЮЯЀЁЂЃЄЅІЇЈЉЊЋЌЍЎЏѠѢѤѦѨѪѬѮѰѲѴѶѸѺѼѾҀҊҌҎҐҒҔҖҘҚҜҞҠҢҤҦҨҪҬҮҰҲҴҶҸҺҼҾӁӃӇӋӐӒӔӖӘӚӜӞӠӢӤӦӨӪӬӮӰӲӴӶӸԱԲԳԴԵԶԷԸԹԺԻԼԽԾԿՀՁՂՃՄՅՆՇՈՉՊՋՌՍՎՏՐՑՒՓՔՕՖḀḂḄḆḈḊḌḎḐḒḔḖḘḚḜḞḠḢḤḦḨḪḬḮḰḲḴḶḸḺḼḾṀṂṄṆṈṊṌṎṐṒṔṖṘṚṜṞṠṢṤṦṨṪṬṮṰṲṴṶṸṺṼṾẀẂẄẆẈẊẌẎẐẒẔṠẠẢẤẦẨẪẬẮẰẲẴẶẸẺẼẾỀỂỄỆỈỊỌỎỐỒỔỖỘỚỜỞỠỢỤỦỨỪỬỮỰỲỴỶỸἈἉἊἋἌἍἎἏἘἙἚἛἜἝἨἩἪἫἬἭἮἯἸἹἺἻἼἽἾἿὈὉὊὋὌὍὙὛὝὟὨὩὪὫὬὭὮὯᾺΆῈΈῊΉῚΊῸΌῪΎῺΏᾈᾉᾊᾋᾌᾍᾎᾏᾘᾙᾚᾛᾜᾝᾞᾟᾨᾩᾪᾫᾬᾭᾮᾯᾸᾹᾼΙῌῘῙῨῩῬῼⅠⅡⅢⅣⅤⅥⅦⅧⅨⅩⅪⅫⅬⅭⅮⅯⒶⒷⒸⒹⒺⒻⒼⒽⒾⒿⓀⓁⓂⓃⓄⓅⓆⓇⓈⓉⓊⓋⓌⓍⓎⓏＡＢＣＤＥＦＧＨＩＪＫＬＭＮＯＰＱＲＳＴＵＶＷＸＹＺ
+
diff --git a/tests/tests/swfs/avm2/string_case/test.fla b/tests/tests/swfs/avm2/string_case/test.fla
new file mode 100644
index 000000000..c5fea5350
Binary files /dev/null and b/tests/tests/swfs/avm2/string_case/test.fla differ
diff --git a/tests/tests/swfs/avm2/string_case/test.swf b/tests/tests/swfs/avm2/string_case/test.swf
new file mode 100644
index 000000000..01cfa443c
Binary files /dev/null and b/tests/tests/swfs/avm2/string_case/test.swf differ