This invention provides a refrigerator oil, a working fluid for a refrigerator, and a method for lubricating a refrigeration system, which can inhibit the creation of deposits attributable to metal working oils remaining within a refrigeration system. The refrigerator oil contains: a polyhydric alcohol ester compound as a lube base oil, and 0.5 to 4.5% by weight of at least one polyoxyalkylene compound. The working fluid for a refrigerator, containing: the above refrigerator oil, and a hydrofluorocarbon refrigerant. A method for lubricating a refrigeration system contaminated with metal working oils, containing a component sparingly soluble in the polyhydric alcohol ester compound or the hydrofluorocarbon refrigerant, or metal working oils, containing a component highly reactive with the polyhydric alcohol ester compound or the hydrofluorocarbon refrigerant, remaining therein, wherein the above working fluid for a refrigerator is used as a working fluid. According to the present invention, occurrence of deposits in the system, especially in a capillary in the system, can be prevented