It started just after 6:30 a.m. at Art's Mini Storage on Stage Coach Road near Highway 49.
Cal Fire and the Madera County Fire Department both sent engines to the scene.
The flames spread through a through a common attic and damaged a total of nine storage units.
"It's sad. Some of it I think insurance will not cover. There's some antiques in a couple of the units and it looks like they've been extensively damage, if not destroyed. There's not a lot that survived the fire," Art's Mini Storage Manager Roger Schneider said.
"On a Labor Day weekend, this is not the way most people wanted to start off their morning, but we're very fortunate that nobody was injured and many of the storage units did not receive any damage," Cal Fire Battalion Chief Nick Schuler said.
Fire investigators say the property has security cameras that may help them figure out how the blaze started. The dollar amount of the damage is not yet known.