Fire crews were called to deal with a blaze at sports changing rooms off Princes Avenue in Roundhay Park at 7pm last night.
Around 15 firefighters from Moortown, Killingbeck and Leeds fire stations dealt with the blaze.
West Yorkshire Fire and Rescue Service said the building was “100 per cent” involved in the fire.
A spokeswoman said: “It was quite an extensive fire. Fire crews worked throughout the night damping down, but they have just left now. Fire investigators are looking into the cause.”