Anaerobic digestion of biomass wastes could have a huge impact on renewable energy requirements. Moreover, it reduces biomass wastes and greenhouse gas emissions. To improve the performance of anaerobic digesters, the co-digestion of different biomass wastes, such as waste activated sludge, microalgae, and agriculture wastes including sawdust, wheat straw, and rice straw has been performed in this study. The results showed that sludge and microalgae have low carbon/nitrogen (C/N) ratios. Meanwhile, the addition of agriculture wastes to sludge and microalgae mixture increased the C/N ratio and improved biogas yield by 179%, 209%, and 265% in the cases of adding sawdust, rice straw, and wheat straw, respectively. Co-digestion with wheat straw showed the highest values of C/N for the feedstock (20.6) and biogas production. Moreover, it recorded the highest reduction values for total solids (48.1%), volatile solids (58.2%), and chemical oxygen demand (77.5%) as compared to the other wastes