In this study, optimization of microwave (MW) pretreatment conditions for anaerobic digestion of green microalgae (Enteromorpha) is carried out by using response surface methodology (RSM). MW power, pretreatment time and liquid-solid ratio were selected as independent variables for optimization. The optimum conditions were achieved at MW power, pretreatment time and liquid-solid ratio of 656.92 W, 5.10 min and 33.63:1, respectively. From these optimum conditions, it was found that MW pretreatment power of about 600 W had better effect. An anaerobic digestion was carried out batch-wise with working volume, operating temperature and mixing rate as 250 ml, 37 °C and 150 rpm, respectively. Optimum conditions provide highest amount of COD and reducing sugar increase of 10,420 mg/L and 0.77-0.79 g/L respectively. The increase in COD and reducing sugar showed that the pretreatment has improved anaerobic digestion of microalgae. The peak biogas production amount of MW pretreated 20:1, 6 min group reached 244 mL whereas the control group only reached 188 mL in total.