The invention relates to a refrigerator oil composition for compression refrigerators with carbon dioxide refrigerant therein, such as car air conditioners, refrigerators, freezers, air conditioners, heat pumps, etc. The base oil of the composition comprises an oxygen-containing organic compound as the essential component and has a kinematic viscosity at 100° C. of from 5 to 50 mm2/sec, a viscosity index of at least 60, and a water content of at most 300 ppm.