A process to lubricate a refrigerator preferably having a sliding portion which is made of an engineering plastic material, or provided thereon with an organic coating film or an inorganic coating film is provided. The process includes contacting sliding parts of the refrigerator with a refrigerating machine oil composition having a base oil containing a polyvinyl ether and/or a polyoxyalkylene glycol derivative as a main component and having a kinematic viscosity of 1 to 8 mm2/s as measured at 40° C. The refrigerating machine oil composition has a low viscosity, an improved energy saving performance, a good sealability and an excellent compatibility with a refrigerant and, therefore, the process can be suitably used in various refrigerating application fields, in particular, in closed-system refrigerators.