A variable capacity rotary compressor includes a housing defining a cylindrical compression chamber therein and having an inlet port and an outlet port communicating with the compression chamber. A rotating shaft is provided with an eccentric part to rotate in the compression chamber. A ring piston is rotatably fitted over the eccentric part such that an outer surface of the ring piston is in contact with an inner surface of the compression chamber. A vane is installed in the housing so as to be in contact with the outer surface of the ring piston and radially reciprocates, and partitions the compression chamber into an intake part and a discharging part. A re-expansion space communicates with the compression chamber, and receives refrigerant therein. A control unit opens or closes an inlet of the re-expansion space to vary a capacity of the rotary compressor.