The four-year-old male rhinos were being cared for at the Centre for Wildlife Rehabilitation and Conservation (CWRC), officials said.
The rhino duo, named Gopal and Hari, were found in the Bauntika and Haldibari areas of the Kohora forest range in 2009.
The rhinos were seen off by KNP Director MK Yadav, Divisional Forest Officer SK Seal Sharma and CWRC Deputy Director Rathin Barman.