Three bacteria, named L2, L3 and L4, were isolated from contaminated cultures of Chlamydomonas reinhardtii strain cc849 in laboratory. The phylogenetic analysis based on 16S rDNA sequences showed that L2, L3 and L4 belonged to genus Stenotrophomonas, Microbacterium and Pseudomonas, respectively. The co-cultivation of isolated L2, L3 and L4 with purified algae, respectively, demonstrated that moderate bacterial concentration did not affect algal growth significantly but improved algal H-2 production obviously. The maximal H2 yields were gained by the co-culture of algae with L2 or L4, about 4.0 times higher than that of the single algal culture. Increased respiration rate or O-2 consumption was the main reason for the enhancement of H-2 yield of the co-cultures. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.