diff --git a/src/kivm/native/java_io_FileOutputStream.cpp b/src/kivm/native/java_io_FileOutputStream.cpp
index eff80b6..fd33b4e 100644
--- a/src/kivm/native/java_io_FileOutputStream.cpp
+++ b/src/kivm/native/java_io_FileOutputStream.cpp
@@ -3,10 +3,56 @@
 //
 
 #include <kivm/kivm.h>
+#include <kivm/oop/primitiveOop.h>
+#include <kivm/oop/arrayOop.h>
 #include <kivm/native/classNames.h>
+#include <kivm/bytecode/execution.h>
+#include <unistd.h>
+#include <cstring>
+#include <kivm/memory/universe.h>
 
 using namespace kivm;
 
 JAVA_NATIVE void Java_java_io_FileOutputStream_initIDs(JNIEnv *env, jclass java_io_FileOutputStream) {
     D("java/io/FileOutputStream.initIDs()V");
 }
+
+JAVA_NATIVE void Java_java_io_FileOutputStream_writeBytes(JNIEnv *env, jobject javaOutputStream,
+                                                          jbyteArray b, jint off, jint len, jboolean append) {
+    static auto CLASS = (InstanceKlass *) BootstrapClassLoader::get()
+        ->loadClass(L"java/io/FileOutputStream");
+    static auto FD_CLASS = (InstanceKlass *) BootstrapClassLoader::get()
+        ->loadClass(L"java/io/FileDescriptor");
+    static auto FD_FIELD = CLASS->getInstanceFieldInfo(CLASS->getName(), L"fd", L"Ljava/io/FileDescriptor;");
+    static auto FD_INT_FIELD = FD_CLASS->getInstanceFieldInfo(FD_CLASS->getName(), L"fd", L"I");
+
+    auto byteArray = Resolver::typeArray(b);
+    if (byteArray == nullptr) {
+        SHOULD_NOT_REACH_HERE();
+    }
+
+    if (byteArray->getLength() <= off && byteArray->getLength() < (off + len)) {
+        PANIC("java.lang.ArrayIndexOutOfBoundsException");
+    }
+
+    auto streamOop = Resolver::instance(javaOutputStream);
+    instanceOop fdOop = nullptr;
+    if (!streamOop->getFieldValue(FD_FIELD, (oop *) &fdOop)) {
+        SHOULD_NOT_REACH_HERE();
+    }
+
+    intOop fdInt = nullptr;
+    if (!fdOop->getFieldValue(FD_INT_FIELD, (oop *) &fdInt)) {
+        SHOULD_NOT_REACH_HERE();
+    }
+
+    int fd = fdInt->getValue();
+    auto *buf = (char *) Universe::allocCObject(sizeof(char) * len);
+    for (int i = off, j = 0; i < off + len; i++, j++) {
+        buf[j] = (char) ((intOop) byteArray->getElementAt(i))->getValue();
+    }
+    if (write(fd, buf, (size_t) len) == -1) {
+        PANIC("java.lang.IOException");
+    }
+    Universe::deallocCObject(buf);
+}