LB films of thermostable hydrogenase from Thiocapsa roseopersicina were prepared on electrodes. Poly-L-lysine was used as a counter ion which stabilizes the protein and improves the protein transfer onto substrates. Both hydrogen production and oxidation activities were observed in the hydrogenase monolayer on substrate. The monolayer film of hydrogenase showed a high thermal stability as in solution, i.e. denaturation did not occur up to 70 degrees C. Electrochemical hydrogen evolution was observed by biasing the ITO electrode on which the LB film of hydrogenase was mounted in the presence of methyl viologen as a mediator.