Biomethanation is a promising method for transformation of organic fraction of municipal solid waste (OFMSW) to valuable energy. In addition, as OFMSW has considerable portion in any community generated solid waste, biomethanation reduces the total waste to be collected, transported and disposed to the landfill. In this study application of laboratory-scale anaerobic baffled reactor (ABR) for production of methane gas through co-digestion of kitchen waste and sewage sludge was investigated. Performance of four ABRs with identical volume of 75 l under hydraulic retention time (HRT) of 3 days and with kitchen waste and sewage sludge mixed at ratio of 100:0, 75:25, 50:50 and 25:75 was compared in terms of methane yield and microorganisms growth. Results indicate that, the ABR containing 75 kitchen waste and 25 sewage sludge had highest volumetric percentage of methane (>80). This amount was relatively reasonable for other samples except sample with 100 kitchen waste ( 20). pH investigation shows sample containing 100 kitchen waste is slow compared to the others in term of higher-molecular-mass compounds breakdown as well as development of both acid formers and methane formers. This signifies that not only the suitable substrate but also proper development of different species of microorganisms is vital in any biomethanation system. © 2012 IEEE.