Alkaline pretreatment and gamma ray irradiation were applied to destroy the refactory structure of waste activated sludge (WAS), and to increase its solubilization. Recovery of carbon source from WAS is for a sludge recycling and organic matter removal. Extraction of extracellular polymeric substrates (EPS) were mainly composed of carbohydrate, protein and humic substance. EPS and soluble chemical oxygen Demand (SCOD) increased as gamma ray irradiation increased from 1kGy to 50kGy. Carbon source extracted from WAS by the combination of gamma ray and alkaline treatment could be used to enhance the biological denitrification rate.