Fr Dermot Maloney required hospital and dental treatment after he was attacked by the gang in Jonesborough, Newry.
He sustained facial injuries including a split lip and damage to his teeth.
At around 11.30pm on Wednesday the priest discovered three youths in the office before they assaulted him and left him locked in a bathroom.
They made off with his wallet containing a small sum of cash.
The priest managed to escape from the bathroom by climbing from a window.
Fr Maloney was too distressed to comment yesterday afternoon.
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