In this study; effect of pH and amount of anaerobic biological treatment sludge (ABTS) on biogas production rate was investigated by co-digestion of cattle manure with ABTS. Laboratory experiments were performed in batch tank reactors at mesophilic conditions using Box-Wilson design method. Temperature and total solid concentration was kept constant. The amount of ABTS and pH were varied between 50-150 g and 6.8-7.8 respectively. Statistical analyses were carried out by the use of Design Expert Trial 7.0.0 program. Maximum biogas production rate obtained at a pH value of 7.28 and the amount of anaerobic biological treatment sludge of 108.17 gram was 1.805 ml/day.g.