Abstract: Gamma irradiation was applied to the saccharification process of seaweed. Seaweed biomass was gamma-irradiated at doses of 0, 50, 100, 200, 500 kGy and then the irradiated biomass was hydrolyzed using sulfuric acid. The concentration of reducing sugar of hydrolysates significantly increased by gamma irradiation. Microscopic images show that gamma irradiation causes structure breakage of the seaweed cell wall. These results indicate that the combined method of gamma irradiation with acid hydrolysis can significantly improve the saccharification process for bioenergy production from seaweed biomass.