This paper describes the development of Co alloy films thinner than 50 nm with high perpendicular magnetic coercivity using an electroless deposition process. In order to obtain these films, we used a Cu underlayer for a heteroepitaxial growth of the Co alloys and an optimized bath composition which included sodium hypophosphite and hydrazine as reductants. As a results, the perpendicular coercivity of the films turned to be higher 3000 Oe at the initial deposition stage with the thickness lower than 80 nm. In particular, the high perpendicular magnetic coercivity of the film as thin as 25 nm thick was obtained. These results indicate that electroless deposition is applicable for formation of the films with high perpendicular magnetic coercivity by optimizing the deposition conditions.