A micromixer using direct ultrasonic vibration is first reported in this paper. The ultrasonic vibration was induced by a bulk lead-zirconate-titanate (PZT; 5 X 4 X 0.2 mm), which was excited by a 48 kHz square wave at 150 V (peak-to-peak). Liquids were mixed in a chamber (6 x 6 x 0.06 mm) with an oscillating diaphragm driven by the PZT. The oscillating diaphragm was in the size of 6 x 6 x 0.15 mm. Ethanol and water were used to test the mixing effectiveness. The laminar flows of ethanol (115 mu L/min) and water (100 mu L/min) were mixed effectively when the PZT was excited. The entire process was recorded using a video camera.