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It is known that the optimal value in anaerobic microbial metabolism is best achieved at a C / N ratio range of 20 to 30. However, protein content use is also widely known for its significant impact in increasing the production of methane gas. Vegetables comparably contain higher amount of protein than cow dung waste, thus it is very potential to be used as the feed of biogas digester. The protein content of cow dung waste of 0.73 gr /100 gr is relatively very low compared to cauliflower, cabbage and mustard greens in which each of which are 5gr /100 gr, 6gr/100 gr, and 2.9gr /100 gr respectively. The method used in this study is the utilization of F2 -EM-4 microorganism activator and low concentration of NaOH mixture in the pretreatment process of vegetable waste feed which aim to increase the C / N ratio meanwhile maintain the protein content itself. The feed mixture of cabbage, cauliflower, and lettuce leftovers is mixed in an optimum C / N composition until it nearly resembles the propotion of the cow dung waste C / N composition. Finally, the addition of GP-7 microorganism activator during the methanogenesis process stage shows satisfying results. Regardless the retention time which takes 10% longer than the process without vegetables waste, the methane gas amount produced in this study is proportional to the one from cow dung waste only.