The hydrolysis of degreased cotton in formic acid has been studied in this paper. Hydrochloric acid is added as a catalyst. The crystalline index of degreased cotton decreases gradually with the increase in treatment time. The effects of the reaction temperature (from 55 to 65 degrees C) and reaction time (from 2 to 9 h) on hydrolysis have been evaluated. The hydrolysis of cellulose and degradation of glucose increase with the increases in reaction time and temperature. The optimal conditions for the hydrolysis of degreased cotton is found to be at 65 degrees C for 5 h. Under the optimal conditions, 23% of the degreased cotton is turned into glucose. The maximum transformation ratio of degreased cotton to reducing sugars is 32%.