Main Line Animal Rescue said a concerned citizen stumbled upon the dog tied to a tree over Easter weekend.
"Every bone in his body was visible to the point where he looked like a skeleton," the Chester Springs, Pa. shelter said on its Facebook page.
The Pennsylvania SPCA worked around the clock to care for the pit bull mix dog before being taken to Main Line Animal Rescue.
Rescuers named him Hal, short for Hallelujah.
Hal weighed only 43 pounds when he was found, but Main Line Animal Rescue told Action News Tuesday night that the dog has already gained 10 more.
Rescuers believe Hal is about three or four years and said he is very sweet and loving.
"What's remarkable about Hal is that he seems to not be shy around people or sad about his state." Nichola Redmond, the site director at Main Line Animal Rescue said. "He's just happy to be around all the people here. So, I think he knows he's getting good care and he's grateful."
Hal was on a refeeding program; he was transitioning to eating bigger meals less frequently and slowly transitioning to a normal diet.
Main Line Animal Rescue said Hal will be available for adoption.