Biogas production from agricultural residue by anaerobic digestion is the most favourable option for providing sustainable energy and reducing the environmental pollution. The experimental methane potential of co-digested rice straw and food waste were measured for different carbon to nitrogen (C/N) ratios in 1 L anaerobic reactor. Co-digesting rice straw with food waste for C/N 25, 30 and 35 almost showed the similar methane yield 294.17 +/- 3.78 mL/g-VSadded, with an increase of 134.53 mL/g-VSadded (71.09%) than mono-digestion. After optimizing the C/N ratio for co-digestion, interactive effect of initial pH and food/microorganism (F/M) ratio were also explored in this study using central composite design - response surface methodology (CCD-RSM). Results from the optimization study showed significant interaction, and validation experiment for optimum condition (C/N 30, pH 7.32, F/M 1.87) showed a methane yield of 323.78 mL/g-VSadded (94.41%), 166.54 mL/g-VSadded higher than the mono-digestion (control). (C) 2019 Elsevier Ltd. All rights reserved.