A refrigerator oil, particularly a refrigerator oil for a hydrofluorocarbon refrigerant, comprising a base oil composed of an oxygen-containing organic compound, such as a polyalkylene glycol and polyester, and a fluorinated silicone oil having a kinematic viscosity of 500 mm.sup.2 /sec or more at 25.degree. C. is disclosed. A process for lubrication of a refigeration system comprising lubricating a compression-type refrigeration system by using the refrigerator oil is also disclosed.By using the refrigerator oil, the foaming phenomenon during boiling of the refrigerant dissolved in the refrigerator oil can effectively be suppressed. In the refrigeration system using the refrigerator oil, effective lubrication can be achieved.