This study investigates the biogas production from cattle manure in a combined microbial electrolysis cell and anaerobic digestion system (MEC+AD). The MEC+AD reactors were operated on semi continuous mode under different voltage applications and different organic loading rates varying from 7 g VS/L.d to 30 g VS/L.d. The study was carried out in two parts. In the first part, combined MEC+AD system and conventional anaerobic digestion were compared in terms of biogas production and organic removal performances at hydraulic retention times of 5, 4, and 3 days to see the effects of voltage application. In the second part, MEC+AD reactors were operated under different voltage applications (0.3, 0.6, and 1.0 V) and organic loading rates at constant hydraulic retention time of 2 days. In terms of biogas production and organic removal rate, MEC+AD reactors were superior to anaerobic control reactor owing to the voltage application. The biogas production of MEC+AD reactors increased from 1.75 to 5.13 L/L/d (71.6-77.8 % CH4) with the increase in organic loading rate. On the other hand, the highest methane yield (0.217 L/g VS) was observed at the lowest organic loading rate of 6.72 g VS/L/d at 5 days hydraulic retention time. The effect of different voltages was not significant in the reactors due to the similar biogas productions and organic removal rates. MEC+AD reactors still operated efficiently even at the highest organic loading rate of 30 g VS/L/d without any instability problem.