This paper presents a polymer-based micropump for liquid control or drug delivery. The dimension of the pump was 20 × 24 × 3 mm 3. A pair of O-ring SU-8 passive valves was fabricated by lift-off technique to control the fluid movement. Micropumps with dimple, bridge, and cantilever valves were studied. The PZT bimorph acted on the polymer membrane to periodically drive fluid. The maximum flow rate was 16.4 ml/min, and the back pressure was 1,525 mmH 2O at 150 V (Vp-p). In frequency sweeping experiments, two flow rate peaks and back pressure peaks were analyzed. Bidirectional flow rate was achieved by changing the valve seat from a one-size hole to a step hole. The maximum backward flow rate was 5.1 ml/min, and the driving frequency was about 355 Hz higher than the forward flow rate driving frequency.