Abstract: This paper reports that the hydrogen evolution in dark and the oxygen evolution by light from intact cells of Spirulina platensis treated with 0.8 mol/l this (pH 8.0) were inactivated, but they were restored after removing tris. The restoration of activity is related to manganese and increased with its amount raised in the liquid medium. If the manganese in medium is too high, the inhibition of hydrogen and oxygen evolution will take place. DCMU, methylamine, hydroxyl, amine hydrochloride which are the inhibitors of PS Ⅱ inhibit not only evolution of oxygen, but also of hydrogen.