Spent mushroom substrate and cowdung co-digested in various proportions in laboratory considering 40 days of HRT. Biogas production from each treatment, its compositional analysis and slurry characteristics were analyzed. The biogas production was found highest in treatment six (T6) when spent button mushroom waste was co-digested with cow dung in 1:3 proportions. The total biogas production at STP from T6 was about 6.54 liters in 40 days from 200 g mixture of selected proportion. The total specific biogas production in L/kg TS and L/kg VS from Treatment T6 within 40 days of biomethanation period was observed as 106.11 L/kg TS and 123.90 L/kg VS respectively. Methane (CH4) & CO2 percentage was found approximately similar in all treatments; although methane percentage was found comparatively better in treatment T6 after treatment T5. After stabilization CH4 percentage was varying in between 54% to 57% in T6. In T6, percentage reduction in total solid and total volatile solids was 11.68% and 13.65% respectively which is highest as compared to other selected treatments after control treatment T5.