Arsonists started a fire in a derelict building in Ingrow last night.
Fire fighters were called to the disused industrial property at about 10pm.
Watch commander Steve Moorhouse, of Keighley Fire Station, said the flames had affected a 10 to 15 square metre area of flooring and wooden joists.
"There have been quite a few fires at this place before," he added. "We were there for about an hour."