The Bee Gees singer checked in to the London Clinic on Wednesday and continues to be monitored by doctors.
A representative for the 62-year-old said in a statement: "Robin is at the London Clinic as part of his treatment and rehabilitation."
Sources told The Sun that doctors have been "astounded at his response to treatment".
Gibb has been receiving chemotherapy following his diagnosis last year.
However, the 'How Deep Is Your Love' star claimed recently that he "feels fantastic" and was deemed well enough to perform at a London Palladium charity concert on February 13.
Watch Robin Gibb perform 'How Deep Is Your Love' with The Soldiers at the London Palladium below: