In this study, 4 different anaerobic digesters were set by keeping the chicken manure ratios as 0%, 30%, 70%, and 100% by completing the remaining portions with cattle manures. According to the results, the highest methane production potentials were 144 +/- 7, 201 +/- 12, 217 +/- 3, 256 +/- 5 L/kg VSadded, respectively. After reaching the highest total nitrogen concentrations in semi continuously operated reactors, methane level has dropped due to free ammonia (as high as 652 mg NH3-N/L) inhibition stimulated by high pH in all reactors. Recovery of the methane production following free ammonia inhibition was greatly succeeded although deficiency in essential trace elements such as Cd and Ni. Nevertheless, it was shown that cattle manure alone can be a good co-substrate for the chicken manure.