Sewage sludge removal via anaerobic digestion provides energy production in addition to waste minimization. Several strategies, such as anaerobic co-digestion, were developed to increase energy production from sewage sludge by improving C/N balance. In this study, anaerobic co-digestion of sewage sludge with an energy crop, namely switchgrass, was evaluated. As a result of studies implemented at different mixing ratios, maximum methane production was measured as 272.06 mLCH(4)/gVS at the mixing ratio of 0.4: 0.6 (sewage sludge: switchgrass). According to modified kinetic models used for interpretation of synergetic and/or antagonistic effects, anaerobic co-digestion has a synergetic effect on biogas production from both biomass.