In order to decompose the refractory structure of waste activated sludge (WAS) and increase its biodegradability, H2O2 pre-treatment and Gamma ray treatment were used in this study. Solubilization efficiency was increased from 4% to 17% based on the SCOD/TCOD ratio. The highest biodegradability could be obtained when the sludge was treated with both Gamma ray and H2O2 simultaneously. Biodegradability of the pre-treated sludge showed linear relationship with the solubilization efficiency.