Abstract: The radioactive spent tributylphosphate (TBP) from nuclear industry has large potential hazards, and its processing is a worldwide problem and the study still stays at the level of theory. In this paper, the solidification by alkali-activated slag (AAS) was proposed aimed at the high alkalinity and organic salt content of spent TBP hydrolysate. The effects of activator content, hydrolysate incorporating amount and curing age on the mechanical properties, water resistance, freeze-thaw resistance, hydration degree, alkalinity, mineral composition, and content of active Al and Si were studied. The results indicate that the AAS reveals prominent superiority in the respect of immobilizing spent TBP compared with ordinary Portland cement (OPC) and slag Portland cement (SPC). The compressive strength of immobilization matrix is 18.90 MPa at 28 d incorporating 14.49% spent TBP hydrolysate, while that of OPC is only 8.69 MPa. The leaching resistance, freeze-thaw resistance and shock resistance of AAS are all much better than that of SPC and OPC.