Ni-Fe-W alloys were obtained by electroplating using an ammoniacal citrate bath with a cation exchange membrane cell. The addition of 8 atom % iron to the Ni-W alloy (Ni78Fe8W14) removed surface microcracks on the deposits and increased the iron content, which was paralleled by an apparent increase in the tungsten content. To improve the microhardness, deposits were heat-treated at various temperatures. The maximum Vickers hardness value of 1350 was obtained after heat-treatment at 500 degrees C. X-ray diffraction analysis revealed that the increasing annealing temperature induced both grain growth and precipitation of new phases, especially NiWO4. Transmission electron microscopy and selected area diffraction observations revealed that annealing at 500 degrees C led to a significant hardening of the deposits due to the precipitation of new phases with nanosized grains. However, as the annealing temperature was increased above 500 degrees C, the microhardness began to fall with increasing grain size.