PURPOSE: To keep the toughness of sintered body base material of iron base, by subjecting the iron base sintered body contg. previously P to carburizing or carburizing hardening so as to restrict the hardening depth at the surface portion.

CONSTITUTION: Iron base material powder mixed with 0.2W1% by wt. P is formed into a desired shape, it is then sintered in a carburizing gas at a temp., e.g., about 900°C. The sintered body is oil quenched and tempered at a temp., e.g., about 1,000° so as to harden the surface of the iron base sintered body. This method exhibits satisfactory curburization controlling effect even when the sintered body is of comparatively low density, and the increase of P within the above described limit is excellently effective.