A Perth man who viciously assaulted his grandmother and raped his half-sister has had his sentence almost doubled following a successful appeal by the state prosecutor.

The man, who cannot be named in order to protect the identities of his victims, was sentenced to six years and six months imprisonment after he pleaded guilty to the rampage in February last year.

The man was resentenced on Wednesday. Credit:Emma Young

However, the state prosecutor appealed his sentence on the basis of his “appalling” conduct.

The court heard the man, then 24, went to his grandparents’ house in Byford on July 6 in 2017, and his grandmother let him inside about 5.30pm.