Si micro-electro-mechanical device with GaN light emitting diode (LED) is monolithically fabricated. The GaN-LED layer was grown by molecular beam epitaxy on Si wafer and the basic properties of the LED were tested. The GaN/Si wafer was micromachined using deep reactive ion etching to fabricate Si electrostatic comb-drive actuator. A light distribution variable device with Si actuator was fabricated from the grown wafer. From those experiments, it is shown that the combination of the GaN crystal growth on Si wafer and the Si micromachining is valuable for a new kind of optical micro-systems.