Tungsten heavy alloys (WHAs) are ideal materials in many fields owing to their excellent physical, chemical and mechanical properties. However, due to the poor machinability of tungsten grains, machining of WHAs encounters many problems, especially severe tool wear and low machining efficiency. To solve the problems, an electrochemical modification method is proposed and applied to 95W-3.5Ni-1.5Fe alloy to remove tungsten grains. The results of morphology observation and component analysis show that Na2CO3 solution is effective for the selective etching of tungsten grains and the potential in oxygen evolution region is suitable. The tungsten grains are converted to WO42- during the modification. Meanwhile, the matrix phase remains and a thin passive film composed of Ni(OH)(2) and Fe2O3 generates on its surface. The porous modified layer has excellent hydrophilicity and its thickness increases linearly with etching time. This modification method performs as an effective pretreatment process for subsequent machining of WHAs to reduce tool wear and improve machining efficiency. (C) 2019 The Electrochemical Society.