A novel electrochemical microactuator was developed, which operates as an active valve. The microactuator consists of an electrochemical cell and a membrane that deflects because of the pressure of oxygen gas generated by electrolysis. Relatively large pressures (up to tens of bars) can be reached with only low energy consumption (in the mu W range). In a first prototype a Cu/aq. 1M CuSO4/Pt system was used in an electrochemical cell with dimensions 2x 2 x 1 mm(3), fabricated with silicon micromachining and thin film deposition techniques. When the actuator was driven at 1.6 V and currents below 50 mu A, pressures of 2 bar could be obtained within seconds, causing membrane deflections in the 30 to 70 mu m range. It was found that, in order to improve the performance of the microactuator, it will be necessary to replace the Cu/Cu2+ electrode. A possible alternative is the Sb/Sb-oxide electrode. This system was studied by cyclic voltammetry and the first results are promising.