A batch anaerobic test was conducted to evaluate the effects of adding high carbon content of corn straw to the digestion of Taihu blue algae to attain an optimal C/N ratio for higher methane yield. The addition of corn straw in algae at a C/N ratio of 20/1 increased methane yield by 61.69% at 325 mL g(-1) VS-1 (compared with 201 mL g(-1) VS-1 of algae digestion alone), followed by C/N ratios of 16/1 and 25/1, all operated at 20 g VS L-1 and 35 degrees C. The results suggest the optimal C/N ratio for co-digestion of algae with corn straw is 20/1. The findings could offer options for efficient methane production and waste treatment. (C) 2012 Elsevier Ltd. All rights reserved.