The tensile mechanical properties and fracture behavior of three tungsten heavy alloys (fine-grained 93W–4.9Ni–2.1Fe–0.03Y; coarse-grained 93W–4.9Ni–2.1Fe; coarse-grained 95W–3.5Fe–1.5Ni, wt%) have been investigated in the temperature range from 25 to 1100°C. The results show that ultimate tensile strength, yield strength, fracture strength and nominal total elongation of the three tungsten heavy alloys are strongly temperature-dependent and in most cases decrease with increasing temperature. Fractographic observations using scanning electron microscopy (SEM) show that the fracture modes of the three alloys evolve from a mixture of W cleavage and matrix phase ductile rupture at low temperatures to a mixture of tungsten/matrix and tungsten/tungsten interfacial debonding failure at elevated temperatures.