The fire in the barn and arena for the Stonegate Farm and Construction complex near Belpre, broke out just after 2 p.m. Friday afternoon.
It destroyed at least one horse, but most of them escaped.
The co-owners of the arena, Karen Heiele and Jim Robertson, were not in the farm at the time of the fire.
"The mechanic, just looked up and saw the whole thing was already engulfed," Robertson told reporters after he arrived on the scene. "It was already gone. There were eight horses; some were leased horses and some were our horses."
Among those using the barn to store horses, was Ohio University's national champion equestrian team. Some of the team members arrived at the scene to determine if any of their horses were lost.
While there's a theory the fire might have been electrical in nature, investigators have not determined the cause of the fire.
Robertson estimates the loss to the structure itself at $50-60,000.