Transition metal phosphates are used as inorganic pigments; however, these materials had a weak point for acid and base resistance. Because lanthanum phosphate is insoluble in acidic and basic solution, the addition of lanthanum cation was tried to improve the acid and base resistance of cobalt phosphate pigment. The lanthanum doped cobalt phosphates were prepared from phosphoric acid, cobalt nitrate, and lanthanum nitrate solution. The additional effects of lanthanum cation were studied on the chemical composition, particle shape and size distribution, specific surface area, color, acid and base resistance of the precipitates, and their thermal products.