North Yorkshire Fire and Rescue Service and North Yorkshire Police were called out to the blaze, which broke out on Kilgram Lane, near Jervaulx Abbey, in the early hours on Sunday (August,9).
Crews from Leyburn, Masham, Richmond and Ripon were called out to reports of the fire at around 2am. The barn, which contained 330 bales of straw, was well alight when firefighters arrived.
NYFRS Group Manager for Harrogate and Craven Districts, Ben Cairns, says nearby residents and farm animals had to be evacuated on the night.
He said: "The barn, measuring approx 25m x 10m, was completely destroyed by fire. An adjacent barn was fire damaged and approximately 150 pigs had to be evacuated. An adjacent holiday cottage was heat damaged and the residents were also evacuated. A number of youths were seen leaving the area at the time of the fire being discovered."
Police are appealing for witnesses and information to assist the investigation, an NYP spokespersons said: "Enquiries are ongoing to determine the cause of the fire and the circumstances surrounding it. At this stage it is being treated as suspicious."
If you have information call 101 or call Crimestoppers on 0800 555111.