Agricultural wastes such as palm oil waste, corn stover, rice straw and wheat straw are some of the wastes that are popular to become feedstocks for anaerobic co-digestion. This is because of their plentiful supply, potential to utilize as a source of biogas, high potential for biogas yields, and low costs. In this study, decanter cake from palm oil mill (OPDC) and sewage sludge were used as substrate to determine the potentiality to produce methane gas from anaerobic co-digestion. Methane yield was analyzed using Excel solver between theoretical yield and experimental yield by using the modified Gompertz Equation. 6400 mL of anaerobic digester was used to conduct the fermentation at mesophilic temperature of 38±1 ⁰C for 30 days. The digester containing sewage sludge and decanter cake mixed at inoculum to substrate (I/S) ratio of 2:1 at 25% of total solid content. Biogas produced was collected and measured using a syringe and transferred into Hungate tube by water displacement method. The biogas composition was measured by gas chromatography (GC). The maximum biogas yield that was produced in anaerobic digester was 5848 mL with the highest methane yield of 581 mL CH4/g-VS at the 14th day. The co-digestion of sewage sludge and decanter cake was converted to methane corresponding to cumulative methane production of 10451 mL CH4/g VS. The experimental yield was compared with theoretical yield by using modified Gompertz. Based on the experimental data, 16748.5 mL of cumulative methane yield was obtained and compared to the cumulative predicted data of 32811.1 mL respectively. In conclusion, decanter cake and sewage sludge have a potential to become substrate in anaerobic co-digestion.