The performance of photo microbial fuel cells (photo-MFCs) with Desmodesmus sp. A8 as cathodic microorganism under different light intensities (0, 1500, 2000, 2500, 3000, 3500 lx) was investigated. The results showed that illumination enhanced the output of the photo-MFC three-fold. When light intensity was increased from 0 to 1500 lx, cathode resistance decreased from 3152.0 to 136.7 Omega while anode resistance decreased from 13.9 to 11.3 Omega. In addition, the cathode potential increased from -0.44 to -0.33 V (vs. Ag/AgCl) and reached a plateau as the light intensity was increased from 1500 lx to 3500 lx. Accompanied with the potential change, dissolved oxygen (DO) within the cathode biofilm increased to 13.2 mg L-1 under light intensity of 3500 lx and dropped to 7.5 mg L-1 at 1500 lx. This work demonstrated that light intensity profoundly impacted the performance of photo-MFC with Desmodesmus sp. A8 through changing the DO. (C) 2013 Elsevier Ltd. All rights reserved.