Biogas is a green energy which can subsidize the energy constraint in one’s country. Biogas production using digesters plants in Ethiopia relay on single substrate and without fermentative microbe inoculation. These and others are challenges to biogas production in the area. Hence, the purpose of this research study was to enhance biogas production using rumen fluid as microbial inoculum during the co-digestion of organic wastes. The study was conducted in Debre Markos town where different organic wastes are available in surplus. Samples were collected from purposefully selected houses. For the biogas fermentation 20L plastic jar under anaerobic conditions was used. The fermentation reaction lasted for 30 days. During the study, two main laboratory activities have been done. Optimizing the rumen fluid amount for better biogas production during fermentation reaction with cow manure. Formulation of best mixes of fruit and vegetable wastes with cow manure for co-digestion. During the anaerobic digestion of organic wastes, the biogas pressure was read as data using a pressure gauge and the produced biogas from the fermentation was collected using a plastic bag (Calamadari) for further analysis. Data analysis was done using SAS software 9.4 versions. One-way ANOVA was done for the parameters recorded from the fermentation reaction. From the physio-chemical analysis, it was observed the pH increased with the time of fermentation starting from a pH value of 6.0 to a maximum pH value of 7.20, and the temperature increased from 18oC to 36oC with the time of fermentation. Both cow manure and FVW had the highest (20.0) TS, and the rumen fluid and FVW had higher percentages of organic carbon and volatile solids which have a direct role in biogas production. Experiment one among the four treatments, containing 37.5% CM, 37.5RF, and 25% tap water (T2) was found to be the best in developing 8.3kpsca gage reading 92.1% methane content of the biogas and the shorter fermentation period. During this experiment, treatment with 7.5L of rumen fluid was found to be an adequate level of inoculum for a 20L fermenter. In the subsequent experiment co-digestion of blended substrates, T3 which contains 18.5% manure, 25% FVW, and 18.5% Tap water produced a higher amount of biogas with high methane (88%) within 27 days. Fermentation reactions having the shortest duration to complete have a strong negative correlation with pressure gage reading(r=-0.91), biogas weight(r=-0.92), and methane content of the produced biogas(r=-0.81). In general, fermentations supplemented with rumen fluid have a faster reaction rate with higher methane content compared to the fermentation reaction devoid of rumen fluid. Keywords: Biogas, co-digestion, Inoculum, pressure gage reading, Reactor, Rumen fluid