diff --git a/javalanglib/src/main/scala/java/lang/StringBuffer.scala b/javalanglib/src/main/scala/java/lang/StringBuffer.scala
index 317e373aef..31ee89a40c 100644
--- a/javalanglib/src/main/scala/java/lang/StringBuffer.scala
+++ b/javalanglib/src/main/scala/java/lang/StringBuffer.scala
@@ -67,6 +67,28 @@ class StringBuffer(private var content: String) extends CharSequence
     this
   }
 
+  def deleteCharAt(index: Int): StringBuffer = {
+    if (index < 0 || index >= content.length)
+      throw new StringIndexOutOfBoundsException("String index out of range: " + index)
+    content = content.substring(0, index) + content.substring(index+1)
+    this
+  }
+
+  /**
+   * @param start The beginning index, inclusive.
+   * @param end The ending index, exclusive.
+   * @param str String that will replace previous contents.
+   * @return This StringBuilder.
+   */
+  def replace(start: Int, end: Int, str: String): StringBuffer = {
+    val length = content.length
+    if (start < 0 || start > end || start >= length)
+      throw new StringIndexOutOfBoundsException(s"Illegal to replace substring at [$start - $end] in string of length $length")
+    val realEnd = if (end > length) length else end // java api convention
+    content = content.substring(0, start) + str + content.substring(realEnd)
+    this
+  }
+
   def setCharAt(index: Int, ch: scala.Char): Unit = {
     if (index < 0 || index >= content.length)
       throw new IndexOutOfBoundsException("String index out of range: " + index)
diff --git a/javalanglib/src/main/scala/java/lang/StringBuilder.scala b/javalanglib/src/main/scala/java/lang/StringBuilder.scala
index e8d9cdbbe9..e8bd2b77df 100644
--- a/javalanglib/src/main/scala/java/lang/StringBuilder.scala
+++ b/javalanglib/src/main/scala/java/lang/StringBuilder.scala
@@ -86,6 +86,28 @@ class StringBuilder(private var content: String) extends CharSequence
     this
   }
 
+  def deleteCharAt(index: Int): StringBuilder = {
+    if (index < 0 || index >= content.length)
+      throw new StringIndexOutOfBoundsException("String index out of range: " + index)
+    content = content.substring(0, index) + content.substring(index+1)
+    this
+  }
+
+  /**
+   * @param start The beginning index, inclusive.
+   * @param end The ending index, exclusive.
+   * @param str String that will replace previous contents.
+   * @return This StringBuilder.
+   */
+  def replace(start: Int, end: Int, str: String): StringBuilder = {
+    val length = content.length
+    if (start < 0 || start > end || start >= length)
+      throw new StringIndexOutOfBoundsException(s"Illegal to replace substring at [$start - $end] in string of length $length")
+    val realEnd = if (end > length) length else end // java api convention
+    content = content.substring(0, start) + str + content.substring(realEnd)
+    this
+  }
+
   def setCharAt(index: Int, ch: scala.Char): Unit = {
     if (index < 0 || index >= content.length)
       throw new IndexOutOfBoundsException("String index out of range: " + index)
diff --git a/test-suite/src/test/scala/scala/scalajs/testsuite/javalib/StringBufferTest.scala b/test-suite/src/test/scala/scala/scalajs/testsuite/javalib/StringBufferTest.scala
index 85409a541d..a034ce67d5 100644
--- a/test-suite/src/test/scala/scala/scalajs/testsuite/javalib/StringBufferTest.scala
+++ b/test-suite/src/test/scala/scala/scalajs/testsuite/javalib/StringBufferTest.scala
@@ -71,6 +71,26 @@ object StringBufferTest extends JasmineTest {
       shouldThrow[StringIndexOutOfBoundsException](initBuf("abcd").insert(-1, "whatever"))
     }
 
+    it("should respond to `deleteCharAt`") {
+      expect(initBuf("0123").deleteCharAt(1).toString).toEqual("023")
+      expect(initBuf("0123").deleteCharAt(0).toString).toEqual("123")
+      expect(initBuf("0123").deleteCharAt(3).toString).toEqual("012")
+      shouldThrow[StringIndexOutOfBoundsException](initBuf("0123").deleteCharAt(-1))
+      shouldThrow[StringIndexOutOfBoundsException](initBuf("0123").deleteCharAt(4))
+    }
+
+    it("should respond to `replace`") {
+      expect(initBuf("0123").replace(1,3,"bc").toString).toEqual("0bc3")
+      expect(initBuf("0123").replace(0,4,"abcd").toString).toEqual("abcd")
+      expect(initBuf("0123").replace(0,10,"abcd").toString).toEqual("abcd")
+      expect(initBuf("0123").replace(3,10,"defg").toString).toEqual("012defg")
+      expect(initBuf("0123").replace(0,1,"xxxx").toString).toEqual("xxxx123")
+      expect(initBuf("0123").replace(1,1,"xxxx").toString).toEqual("0xxxx123")
+
+      shouldThrow[StringIndexOutOfBoundsException](initBuf("0123").replace(-1,3,"x"))
+      shouldThrow[StringIndexOutOfBoundsException](initBuf("0123").replace(4,5,"x"))
+    }
+
     it("should respond to `setCharAt`") {
       val buf = newBuf
       buf.append("foobar")
@@ -151,6 +171,26 @@ object StringBufferTest extends JasmineTest {
       expect(s"${js.undefined}").toEqual("undefined")
     }
 
+    it("should respond to `deleteCharAt`") {
+      expect(initBuilder("0123").deleteCharAt(1).toString).toEqual("023")
+      expect(initBuilder("0123").deleteCharAt(0).toString).toEqual("123")
+      expect(initBuilder("0123").deleteCharAt(3).toString).toEqual("012")
+      shouldThrow[StringIndexOutOfBoundsException](initBuilder("0123").deleteCharAt(-1))
+      shouldThrow[StringIndexOutOfBoundsException](initBuilder("0123").deleteCharAt(4))
+    }
+
+    it("should respond to `replace`") {
+      expect(initBuilder("0123").replace(1,3,"bc").toString).toEqual("0bc3")
+      expect(initBuilder("0123").replace(0,4,"abcd").toString).toEqual("abcd")
+      expect(initBuilder("0123").replace(0,10,"abcd").toString).toEqual("abcd")
+      expect(initBuilder("0123").replace(3,10,"defg").toString).toEqual("012defg")
+      expect(initBuilder("0123").replace(0,1,"xxxx").toString).toEqual("xxxx123")
+      expect(initBuilder("0123").replace(1,1,"xxxx").toString).toEqual("0xxxx123")
+
+      shouldThrow[StringIndexOutOfBoundsException](initBuilder("0123").replace(-1,3,"x"))
+      shouldThrow[StringIndexOutOfBoundsException](initBuilder("0123").replace(4,5,"x"))
+    }
+
     it("should respond to `setCharAt`") {
       val b = newBuilder
       b.append("foobar")