In the present study, the microstructure and properties characteristics of W-20Cu nano-crystallite composites were investigated. Characterization techniques like XRD and SEM have been used to study the crystallite size of W-Cu powder obtained by mechanical alloying. As well as, the effect of milling time on the microstructure and properties of W-20Cu composites was discussed. The results show that with increasing milling time, the crystallite size of W-Cu composite powder decreased and kept steady at last, and the crystallite size of W(Cu) solid solution was 6.6 nm for milling 20 h. The microstructure of W-20Cu composites became homogeneous and tungsten crystallite size became fine. The relative density and bending strength of W-20Cu composites increased. The value of thermal conductivity peaked when milling time was 20 h.