The dog knocked the boy over and was shaking him, breaking his arm, the court heard.
Steven Michael Price, of Orchard Close, Church Stoke, Powys, admitted two counts of being the owner of a dog dangerously out of control which caused injury.
At Mold Crown court on Thursday Price, 31, received a 16 month jail sentence. Judge Nicola Jones ordered that he serve half of the sentence.
She also ordered the destruction of the dog and banned Price from keeping animals for 10 years.
The court was told that the attack happened in November last year when the dog got out.
It bit a boy, playing with friends nearby, and only let go when it was called off by Price.
The boy needed surgery for fractures to his arm.
Judge Jones was told it was the second time the dog had attacked the boy, the first causing minor injuries and no complaint was made.
Since the attack Price had put high fencing up around his garden, the court heard.