Hydrogenase which catalyzes the production and consumation of gaseous H₂ in the presence of cytochrome C₃ was purified from Desulfovibrio desulfricans. This particulate enzyme was solubilized in Tris-HCl buffer containing Triton X and sodium deoxycholate after sonication. This was further purified by ultracentrifugation (100,000×g) of sonicate, gel filtration on Sephadex G-150, ion-exchange on DEAE-cellulose and isoelectric focusing. Its molecular wight was estimated to be 120,000 by gel filtration on Sephadex G-200 column chromatography and showed maximium activity around pH 7.0. This enzyme catalyzes the H₂ evolving reaction of methyl viologen which is an artificial electron carrier of ferricytochrome C₃. Its Km value was 5.1×10^(-5) M but it was expected to show decrease according to the increase of salt concentration. pI value estimated by isoelectric focusing was 6.1 and it showed rather stable property upon heat inactivation. The enzyme was inhibited by metal complexing agents such as NaN₃, EDTA and KCN, but showed significant activation effect by metal ions such as Fe^(3+) and Fe^(2+).