A study has been investigated on the effect of mechanical properties (tension strength, rotary bending fatigue strength, wear resistance, hardness) according to the carbide particle size variation by the treatment of 1) quenching tempering, and 2) quenching, subzero treatement and tempering. The material used in this investigation was a typical bearing steel, high C high Cr, AISI E 52100. The result obtained in this study were as follows : (1) Finer the carbide particle size increasing the hardness and retained austenite in same quenching condition. (2) Finer the carbide particle size reduced the tension and rotary bending fatigue which were resulted from austenite grain growth and carbide precipitation on grain boundry that induced by carbide refine heat treatment. (3) Finer the carbide particel size increasing the wear resistance which were resulted by uniform distribution of carbide and increased hardness induced by microstructural uniform hardenability of matrix. (4) When the carbide particles were refinded, subzero treatment is effective only wear resistance and hardness.