This paper investigated anaerobic co-digestion of cattle manure and raw algae with and without adding activated sludge as co- substrate and under different substrate ratios. The results showed that the co-digestion of cattle manure with raw algae led to a maximum methane yield of 294 mL/g VS at a CM:A ratio of 70%:30%. While co-digestion of cattle manure and raw algae diluted with tap water under CM:A ratio of (70%:30%) resulted in a methane yield of 97 mL/g VS. In the co-digestion runs conducted with the same feedstock and inoculated with activated sludge, little methane was produced. The values of pH and (N-NH3) showed no inhibitory effect. The kinetic study revealed that the maximum methane yield was 32.4 (mL/g VS.d), 332 (mL methane/g VS) respectively. The lag time ranged from 0 to 3 days. The Response surface methodology showed that methane production could be represented by a second-order polynomial.