To provide a manufacturing method for carburized parts where steel parts composed of a high strength case hardened steel to which Ti is added are carburized and are thereafter subjected to rehardening, thus old austenitic grains are positively ultra-fined, so as to improve the strength thereof.

The manufacturing method for high-strength carburized parts comprises making steel parts composed of a case hardened steel including, by mass, 0.10 to 0.35% C, 0.03 to 0.50% Si, 2.0% or less Mn, 0.020% or less N, and 0.005 to 0.05% Al, further including one or more kinds selected from 0.05 to 0.2% Ti, 0.02 to 0.10% V and 0.02 to 0.10% Nb, and the balance Fe with unavoidable impurities into a steel having a martensitic structure in which old austenitic grains are fined to No.11 prescribed in JIS G0551 or finer, carburizing the steel parts formed from the steel, and thereafter performing rehardening to form the martensitic structure with fined grains to No.11 of JIS G0551 or finer therein.