An experimental study of electroless cobalt-zinc-phosphorous plating films is presented. The results obtained are as follows; 1) The zinc content of the cobalt-zinc-phosphorous films varied from 0 to 11% with zinc sulfate concentration in the solution. 2) Cobalt-zinc-phosphorous films exhibited coercive force ranging from 1600A/m (20 Oe) to 88000A/m (1100 Oe) depending on the plating conditions and high coercive force above 80000A/m (1000 Oe) was achieved for 10μm thickness films. 3) Incorporation of zinc into the cobalt-phosphorous films changed its structure such as particle size, anisotropy and isolation of particles. The modification of magnetic properties could be explained in terms of these film structure changes.