Firefighters were called to private hospital Sherwood House, on Rufford Colliery Lane, Rainworth, shortly after midnight, after reports the building was on fire.
Around 30 residents and ten members of staff were evacuated from the two-floor building after the fire took hold in a ground floor dormitory.
Fire crews used one hose reel jet to extinguish the fire and a ventilation fan to clear the smoke.
A spokesman for Cambian Group, which runs the hospital, said the fire is believed to have been started by a resident in their bedroom.
He added: “We’re thankful that all residents and staff are safe and uninjured after the fire, they returned to their rooms by 2am.
“We are as always grateful for the excellent response of the emergency services and the professionalism of the staff dealing with this matter.
“The hospital is back to running as normal with residents not being impacted other than a reduced night’s sleep.”
A service spokesman confirmed crews from Mansfield, Blidworth and Edwinstwe attended the fire.
He said: “Fortunately the fire had been contained to one room on the ground floor. An area of the premises was evacuated as a precaution.
“The cause of the fire is currently being investigated.”
The incident was declared closed by the fire service at 1.24am.