Fruit and vegetable wastes are produced in large quantities in Iran, and constitute a source of nuisance in municipal landfills. The objective of this study was to optimize the applications of anaerobic digestion for the treatment of municipal organic wastes. We studied the effect of organic loading rates on anaerobic digestion of vegetable wastes. The complete-mix, pilot-scale digester with working volume of 70 l was used. The experiments were conducted at 34oC with a fixed hydraulic retention time of 25 days. The digester was operated at different organic feeding rates of 1.4, 2 and 2.75 kg VS/(m.d). The biogas produced had methane composition of 49.764% and biogas production rates of 0.12-0.4 m/(kg VS). The reactor showed stable performance with highest biogas production (0.4 m/kg VS) and VS reduction of around 88% during loading rate of 1.4 kg VS/(m3.d). The chemical oxygen demand (COD) reduction, VS removal and methane concentration in biogas was decreased when the organic loading rate was increased. Based on the data obtained from this study, OLR of 1.4kg VS/(m.d) is suggested as design criteria with biogas production rate of 0.4 mbiogas/(kg VS).