-7Ni-3Fe heavy alloy was prepared from the tungsten powders doped with different amounts of trace silicon. The behavior of trace silicon in the tungsten heavy alloy was investigated by using scanning electron microscope GEM) and X-ray photoelectron spectrom etry (XPS). The results showed that part of the trace silicon in the form of dispersed SiO2 particles was distributed in the binder phase of the alloy and the remaining in the state of elemental silicon was distributed in the tungsten grains forming a solid solution. It was found that the tungsten grains in the alloys prepared from undoped tungsten powders were covered by a thin layer of WO2 but no WO2 was detected in the alloys prepareds from doped tungsten powders. The mechanism of the formation and elim mation of WO2 was discussed.