Firefighters were first called to the barn in the village of Ryhill, seven miles outside Wakefield, just after 8pm last night.
No people or animals were inside the 2,500 sq m barn in Station Road, which is used for storage of machinery.
Pumps from South Kirkby, Wakefield, Pontefract, Featherstone, Normanton and Cudworth were all involved in the response.
Three large jets, three ground monitors and one hose reel were used by firefighters.
Two pumps are still at the scene this morning.