A novel micro-safety valve for portable hydrogen fuel cells has been designed, fabricated and characterized. This device is intended to prevent over-pressure on the hydrogen side of the fuel cell. A careful study of its sealing properties has been conducted under conditions at which it is nearly open. The leakage rate depending on the size of the sealing surface and on the material of the gasket ( fluorocarbon and parylene films) has been investigated using hydrogen gas. The experimental results show that small sealing surfaces lead to small leakage rates and that the parylene films are easily damaged, leading to important leakage rates. Moreover, it is shown that the resistance to flow of the device is diminished by reducing the width of the valve nozzle.