<P><B>Abstract</B></P> <P>Photosynthetic hydrogen production from organic wastewaters using immobilized mixed culture with photosynthetic bacteria (PSB) was studied. A PSB consortium was immobilized by alginate matrix to form granules. The so-yielded granules exhibited minimal diffusional resistances to substrates and to illumination penetration but still produced more hydrogen from synthetic wastewater than the free cells at identical experimental conditions. Optimal granule size, cell loadings, and cell ages for granules and the minimum substrate concentration and maximum illumination intensity requited to maximize hydrogen production were studied. The applied alginate matrix can provide shield to embedded cells from external challenges, likely the produced proton gradients from the surroundings.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Photosynthetic H<SUB>2</SUB> production from immobilized cells was studied. </LI> <LI> Immobilized cells produced more H<SUB>2</SUB> than free cells. </LI> <LI> Optimal granule size, cell loadings, and cell ages for granules were reported. </LI> <LI> Minimum substrate concentration and maximum illumination intensity were reported. </LI> <LI> Alginate matrix can provide shield to embedded cells from external challenges. </LI> </UL> </P>