Tungsten heavy alloys with different ratios of Mo and Ni-Fe matrix were liquid-phase' sintered to investigate their microstructural evolution. Specimens were sintered at 1500°C for 240 minutes and then were either furnace-cooled or water-quenched. The microstructures of the sintered specimens were examined employing SEM. EMPA. DTA. XRD and TEM. Results indicated that increased Mo in the alloy promoted the formation of a (W,Mo)(Ni,Fe) type intermetallic compound in the furnace-cooled condition. It was a monoeutectic reaction when the added Mo content was higher than 49at.%, or a eutectic reaction when this value was between 37at.% to 49at.%. When Mo was added between 25at.% to 37at.%. the precipitation of the intermetallic compound took place by either a eutectoid or peritectoid reaction. No intermetallic compound was found for the Mo adding level being lower than 15at.%. In the water-quenched condition, a lamellar structure with a thickness around 100nm to 200nm was observed in the specimen whose Mo addition was over 27at.%. The lamellar structure was very tiny and uniformly dispersed in the matrix, which could be a reinforcing phase for the matrix phase.