The analogous rhenium effect of manganese in tungsten-molybdenum alloys was investigated. Nine tungsten alloys were prepared (W – X Mo – Y Mn, X = 5, 10, 15 at%, and Y = 2, 5, 8 at%). Samples were sintered for 1 hour at 1350°C or 1425°C. Besides the tungsten phase, the X-ray diffraction patterns and back scattered electron images show a manganese rich phase which is observed in all samples, while an oxide was also observed in those samples sintered at 1425°C. The slight reduction in the lattice parameter of the tungsten phase is not consistent with the molybdenum or manganese content. The relative densities are 65-80% compared to theoretical due to closed porosity and incomplete reduction. Those alloys containing 5 at% manganese show a decrease in the Vickers hardness. This decrease, however, is about equal to one standard deviation of the measurement.