A high-strength composition iron powder is prepared by mixing an iron base powder with 0.5 to 3.0 mass % of an Fe—Mn powder having a particle diameter of 45 μm or less and a Mn content in the range of 60 to 90 mass %, 1.0 to 3.0 mass % of a Cu powder, 0.3 to 1.0 mass % of a graphite powder, and 0.4 to 1.2 mass % of a powder lubricant for die-forming while adjusting the ratio of the amount of Mn contained in the Fe—Mn powder to the amount of the Cu powder in the range of 0.1 to 1. The high-strength composition iron powder is press-formed and sintered at a temperature equal to or higher than the melting point of Cu to produce a high-strength sintered part having a tensile strength of 580 MPa or higher without using expensive alloying elements such as Ni and Mo.