Brandon Poole of Long Creek said he and his family were driving in their truck when they spotted the box and decided to investigate, WBTW-TV, Myrtle Beach, S.C., reported Tuesday.
"I thought it was little puppies in that little box, so I got closer to it, I noticed I heard squealing so I thought it was baby pigs. I got closer and picked one up. It was three baby bears," Poole said.
Poole, who said he had previously worked at a wildlife ranch but had never held a bear in his hands before, took the cubs to the firehouse where he works as a volunteer firefighter.
"I put them in the truck with us and got up here to the firehouse and called the game warden because I couldn't let them freeze that night. It got real cold. They could have died," Poole said.
He said the incident was thrilling for his young daughters.
One of the cubs was taken to the historic Charles Towne Landing in Charleston, S.C., while its siblings were taken to the Appalachian Bear Rescue in Knoxville, Tenn.
"It felt good, I'm kind of trained to save lives and help, so it felt real good to me," Poole said.
Investigators said they do not know how the bears ended up in the box at the side of the road.