<p>The heat-treating oil composition of the present invention is characterized by comprising a mixed base oil containing a low-boiling base oil having a 5% distillation temperature of from 300 to 400°C in an amount of not less than 5% by mass but less than 50% by mass, and a high-boiling base oil having a 5% distillation temperature of 500°C or higher in an amount of more than 50% by mass but not more than 95% by mass. There is provided a quenching oil composition capable of exhibiting a less fluctuation in hardness or quenching distortion of a metal material treated therewith even when a large number of the metal materials are quenched therewith at the same time.</p>
