Biodegradability of synthetic and real kitchen wastes was assessed in batch assays, under different solid contents between 1,8 and 24% and waste/inoculum ratios between 0,2 and 29 VSwaste/Vsseed sludge. Methanization rate and cumulative methane production from synthetic wastes simulated with different blends of protein, carbohydrates, fat and cellulose were compared. Although the excess of protein, carbohydrates and cellulose enhanced the biodegradability by 16 to 48%, the excess of fat reduced the maximum methane production rate and the biodegradability in 70 and 18%, respectively. The ratio waste/seed was found to be a critical parameter especially for solids content higher than 5%, since the biodegradability and the methane production rate increased significantly when the waste/seed ratio decreased from 1.35 to 0.2 g VS/gVS. The real kitchen waste was more biodegradable than the synthetic waste. However both produced methane at similar rates in batch assays for a waste/seed ratio of 1.35 gVS/gVS.