An osmotic microbial fuel cell (OsMFC) was used for simultaneous thickening and digestion of waste activated sludge (WAS) and converting chemical energy of WAS to clean electricity. The results show that with the load of external resistance of 470 Ω, the stable voltage output and power density reach 200~212 mV and 217~244 mW·m-3, respectively. Due to the use of forward osmosis(FO) membrane, the volume of initial WAS is decreased by 41.3% at the end of operation, and 58.7% of the water in WAS is recovered in the draw solution. During 24 d operation of OsMFC, the total destruction efficiencies of total chemical oxygen demand, mixed liquor suspended solids and mixed liquor volatile suspended solids are approximately 22.2%, 32.8% and 47.6%, respectively. OsMFC brings new visions for energy recovery and resource reclamation from WAS.