Emergency services were alerted to the fire at the giant barn at Naturbruksgymnasium high school in the town Ytterjärna at about 2.30am.
Firefighters from six nearby stations rushed to the rescue, but the barn’s structure had crumbled by morning.
“Now we just have minimal presence on site – one firetruck and two staff – to make sure the remains of the fire don’t spread,” emergency service spokesman Roger Magnusson told the TT news agency.
He said the cause of the fire was yet to be determined.
“When we arrived the barn was more or less entirely engulfed by fire so it is difficult to even say where it started,” said Magnusson.
“The other two buildings on campus that contain a workshop, classrooms, a hay loft, and stables seem to be unaffected,” he added.
No people were hurt in the blaze.
The agricultural high school is owned by the Nibble Foundation (Nibblestiftelsen), which focuses on biodynamic milk production.
Ytterjärna and its environs are home to many agricultural and educational establishments inspired by the anthroposophic movement.