The effects of hot working parameters on flow stress and microstructure of GH864 superalloy were studied by isothermal compressive deformation at deformation temperatures from 1000 to 1160 oC, strain rates of 1 and 10 s-1 and engineering strain of 30%, 50% and 70%. The results show that the deformation temperature has great influence on the ultimate as-heat treated grain size and morphology of carbides on grain boundary. When the temperature is below the γ′ precipitation temperature, the dynamic recrystallization capability is bad. While when the temperature is high enough to resolve MC carbides, severely duplex grain structure and feather-like carbide around smaller grains can be easily formed because of the non-uniform pinning effect of re-precipitated fine MC particles on grain boundary, and all these unfavorable characteristics can be partially eliminated by improving hot deformed structure through increasing strain and decreasing strain rate. The ideal deformation temperature should be confined between γ′ precipitation temperature and dissolution of MC carbide