A hollow fiber degassing membrane (DM) was applied to enhance organic matter degradation and methane gas production of anaerobic granular sludge process by reducing the dissolved hydrogen gas (D-H-2) concentration in the liquid phase. DM was installed in the bench-scale anaerobic granular sludge reactors and D-H-2 was removed through DM using a vacuum pump. Degasification improved the organic matter degradation efficiency to 79% while the efficiency was 62% without degasification at 12,000 mg L-1 of the influent T-COD concentration. Measurement of D-H-2 concentrations in the liquid phase confirmed that D-H-2 was removed by degasification. Furthermore, the effect of acetate concentrations on the organic matter degradation efficiency was investigated. At acetate concentrations above 3 g L-1, organic matter degradation deteriorated. Degasification enhanced the propionate and acetate degradation. These results suggest that degasification reduced D-H-2 concentration and volatile fatty acids concentrations, prevented pH drop, and subsequent enhanced organic matter degradation.