Fire crews were called to The Merchants Manor Hotel in Falmouth on Saturday morning to a report of a sauna on fire.
Two appliances from Falmouth and one from Truro were called at 11:38am.
A fire service report said: "The hotel was evacuated by staff and guests and on firefighters entry to the building a small fire in a sauna was located.
"Crews used two breathing apparatus, one hose reel and one carbon dioxide fire extinguisher to extinguish the fire."
Nick Rudlin, the hotel owner, said: "On Saturday March 8, Falmouth firefighters were called to Merchants Manor hotel at 11.35am in response to a fire in the hotel's sauna.
"All staff and guests were evacuated promptly and firefighters put out the small fire very quickly.
"The sauna, which is regularly serviced, remains closed while investigations are underway as to the cause."