Cassava pulp (CP), a by-product of the tapioca starch industry, has been recognized as a high potential substrate for bio-gas production due to its high carbon content. In this work, co-digestion between CP and distiller stillage (DS) was investigated with the main objective to improve the system stability as well as to enhance the biogas production. The effect of five different CP:DS ratios including 1:0, 1:0.5, 1:1, 0.5:1, and 0:1 based on volatile solids (VS) was carried out. The result showed that the co-digestion of CP and DS is a promising approach for increasing the cumulative methane yield by 65.57%–222.19% compared to the digestion of CP alone. The highest methane yield of 685.10 ml/g VS was obtained at the CP:DS of 1:1. The bacterial and archaeal communities were analyzed by denaturing gradient gel electrophoresis. The bacterial community of CP:DS ratio was dominated by Bacteroidetes, Firmicutes, and Chloroflexi phylum whilst Methanosarcina (Methanosarcina barkeri) dominated the methanogenic archaeal community. This work demonstrated the adaptation of co-digestion resulting in a higher methane production with a higher stability of the system. The result could pave a way for a highly efficient co-digestion system in a larger scale biogas production. © 2021 American Institute of Chemical Engineers.