Laser surface alloying (LSA) was used to synthesize iron-tungsten alloy on mild steel substrate. The slurry of tungsten powder 1.28 mu m in average diameter was made and a uniform layer of the slurry was applied onto substrate using thin layer chromatography method. Thickness of powder layer was varied from 0.2 mm to 0.6 mm. The surface was melted using beam oscillated CO, laser. When impinged energy density is selected to be 93 W mm(-2) or 81 W mm(-2), the microhardness of the obtained iron-rich alloying layer is 330-430 HV. It increases up to 630 HV through heat treatment in hydrogen atmosphere at a temperature of 873 K for 5 h and successively at 973 K for 5 h.