Abstract: In the conversion of cassava starch dregs to biogas, there are some difficult problems in pretreatment process, such as higher cost and the inhibition of the catalyst used for subsequent anaerobic digestion. Two different treatment methods for hydrolysis of cassava starch dregs, with hot water or dilute HNO₃ at high temperature, were respectively used to transfer organic matters into the liquid phase from the solid phase, in order to achieve the dissolving of the biomass. The results showed that higher temperature benefited the hydrolysis of cassava starch dregs, but it led to the decrease of biodegradability of hydrolysate due to the monosaccharide degradation. Using dilute nitric acid could catalyze the hydrolysis process and also improve the biodegradability of hydrolysate, and the value of BOD₅/COD_Cr of hydrolysate could rise from 0.48 up to 0.64 at 150 ℃ in 5 min compared with the condition of hot water.