Gellan gum was irradiated by 60Co γ-rays at 0-175 kGy in dry atmosphere. The molecular weight, molecular weight distribution, structure, solution pH value, and gel strength of gellan gum were determined and characterized using gel permeation chromatography（GPC）, fourier-transform infrared spectra（FT-IR）, texture analyzer（TA.XT plus） and so on. The results show that the weight average molecular weight of gellan gum decreased from 440 kDa to 70 kDa at absorbed dose of 175 kGy, and its water solution cannot form gel under certain conditions. It reveals that the molecular weight and gel strength of gellan gum decrease gradually with increasing absorbed doses, and the degradation products exhibit antioxidant activities.