<P><B>Abstract</B></P><P>Hydrogen production was studied using immobilized green alga <I>Chlorella</I> sp. through a two-stage cyclic process where immobilized cells were first incubated in oxygenic photosynthesis followed by anaerobic incubation for H<SUB>2</SUB> production in the absence of sulfur. <I>Chlorella</I> sp. used in this study was capable of generating H<SUB>2</SUB> under immobilized state in agar. The externally added glucose enhanced H<SUB>2</SUB> production rates and total produced volume while shortened the lag time required for cell adaptation prior to H<SUB>2</SUB> evolution. The rate of hydrogen evolution was increased as temperature increased, and the maximum evolution rate under 30mM glucose was 183mL/h/L and 238mL/h/L at 37°C and 40°C, respectively. In order to continue repeated cycles of H<SUB>2</SUB> production, at least two days of photosynthesis stage should be allowed for cells to recover H<SUB>2</SUB> production potential and cell viability before returning to H<SUB>2</SUB> production stage again.</P>