In this study, the 95W heavy alloys of 3/7, 5/5 and 7/3 of Ni/Fe ratio were sintered at the temperature range between 1420 and $1480^{circ}C$ for 1h and their microstructures were discussed for an effect of the ${mu}$-phase $(Fe_7W_6)$ on the microstructure. The ${mu}$-phase was observed in the only 95W-1.5Ni-3.5Fe alloy of 3/7 and it is thought to be formed and grown from the surface of the W particle. The W particle was surrounded with the ${mu}$-phase and there were only the W particles and this phase without Ni-Fe-W matrix at the most part. The ${mu}$-phase changed the interphase structure in the alloy and the grain growth of the W was suppressed because of interrupting the solution-reprecipitation of the W. The W content in the matrix was considered to be lowered due to the interruption of the solution-reprecipitation and the formation of the ${mu}$-phase in the matrix.??????楮最