Disclosed is a base oil comprising polyol ester, wherein the polyol ester is synthesized using: a polyhydric alcohol containing 5 or more hydroxyl groups; a first fatty acid as a linear fatty acid having 4 to 6 carbon atoms; a second fatty acid as a branched fatty acid having 4 to 6 carbon atoms; and a third fatty acid as a linear or branched fatty acid having 7 to 10 carbon atoms, wherein the polyol ester is used together with a refrigerant having a global warming potential (GWP) of 0 to 2,500, and has a kinematic viscosity at 40°C (KV40) in a range of 95 to 105 cSt. Further, a refrigerating machine oil composition containing the base oil is provided.