The confrontation happened early Sunday morning in the 2600 block of North 7th Street in North Philadelphia.
Police say three men followed a bar owner home.
When the armed men demanded cash, the bar owner pulled out his own gun and fired.
The bullet injured one of the suspects and knocked the gun right out of his hand.
That suspect is in serious condition at Hahnemann Hospital.
The other two suspects fled the scene.
The bar owner was not hurt.
Police say the bar owner does have a permit to carry a gun.