The man was mauled by one or both of the captive-bred grizzly bears at the Animals of Montana facility north of Bozeman, Sheriff Brian Gootkin said.
The victim's name wasn't immediately released, but officials said he's originally from Pennsylvania.
Chuck Watson, attorney for Animals of Montana's owner, Troy Hyde, told the Bozeman Daily Chronicle the grizzly bear had to be put down in order to recover the victim.
"It's obviously a tragic situation, and I don't think we'll ever know exactly what happened," Watson said.
Animals of Montana provides captive-bred animals for photography shoots and motion pictures, ranging from African lions and minks to badgers and bobcats. The company's website said it had three grizzly bears.
The man's death is being investigated by the sheriff's office and Montana Fish, Wildlife and Parks wardens.