This study investigated the possibilities of improving methane yield production from, the anaerobic co-digestion of wheat straw (WS) and primary sludge (PS). The batch experiment was conducted under mesophilic conditions. Different mixtures of WS and PS depending on its C/N ratio were carried out to investigate the optimum C/N ratio for effective methane production. The cumulative methane yields (CMYs) for co-digestion of PS with WS at C/N ratios of 35, 25, 20, 15 and 10 were 1.29, 1.62, 1.33, 2.44 and 2.16 time than digesting PS alone, respectively. The maximum CMYS was observed at C/N ratio of 15 with an increase of 89 %, 50.93 %, 83.61 % and 13.12 % compared with the other C/N ratio of 35, 25, 20 and 10 respectively. This result showed the positive synergy of co-digesting of PS and WS for methane production caused by improving the C/N ratio of the feed stock.