PURPOSE: To produce powder sintered parts with the corrosion resistance improved by coating the surface of a ferrous powder sintered member and impregnating the pore with a silicophosphate polymer consisting essentially of sodium silicate and phosphates.

CONSTITUTION: A silicophosphate polymer is prepared from an aq. soln. (about 20-50wt.% concn.) contg. 10-70 pts.wt. of sodium silicate and 1-40 pts.wt. of a phosphate (sodium tripolyphosphate, etc.). The surface of a ferrous powder sintered member is coated with and its pores impregnated with the polymer, and then the member is heated to about 70-100°C, coated and filled with the polymer so that the coat content is controlled to ≥about 50g/m2 and to ≤about 500g/m2 when the transparency of the appearance is needed. Consequently, the corrosion resistance of the ferrous powder sintered parts is improved by an inexpensive coating and impregnating agent.