The objective of the present study is to improve the biohydrogen production from marine macroalgae (Ulva reticulate) by acidic - hydrogen peroxide (H2O2) induced microwave (AHMW) pretreatment. Higher soluble chemical oxygen demand (SCOD) release of 1450 mg/L and its liquefaction rate of 30.2% was achieved in microwave (MW) pretreatment with treatment time period of 15 mins. Varying concentration of H2O2 from 0.003 to 0.03 g/g TS were used in the optimal microwave power (40%) to enhance the organic release in H2O2 induced microwave pretreatment (HMW). Maximum liquefaction of 33.9% was obtained at the H2O2 concentration of 0.024 g/g TS. The combined HMW pretreatment under acidic (pH 4-6.5) show synergistic effect on organic release. At optimal pH 5, AHMW pretreatment shows the SCOD release of 1850 mg/L with its liquefaction of 38.5% at time of 10 min. Therefore, AHMW pretreatment significantly reduce the treatment time and increase liquefaction when compared to MW and HMW. The maximum biohydrogen production was observed as 92.5 mL H-2/g COD in AHMW pretreatment.