Rice straw is most abundant lignocellulose biomass in the environment. In this paper, effect of the sulfate in the anaerobic digestion of rice straw has been identified. Biodegradability of the rice straw has been assessed in terms of production of soluble compounds. The parameter such as Chemical Oxygen Demand (COD), Total Reducing Sugar (TRS), and Volatile Fatty Acids (VFA) has been analyzed to observe the biodegradability. Two set of experiments were run for the HRT of 55 days, first set where sulfate is present (Reactor R1), while second set where sulfate is absent (Reactor B1). The residual amount of COD, TRS and VFA were lesser in Reactor R1 (1851±117, 1299±148, 500±70 respectively) in comparison of Reactor B1 (3100±117, 1953±234, 750±110 respectively), within HRT of 55 days. By comparing both of results, it is revealed that the presence of sulfate were found to beneficial for digesting the rice straw under the anaerobic condition.