A Catholic priest who sexually abused a young girl on four separate occasions in 1974 has been jailed for four months.

Anthony Colbourne pleaded guilty this morning to indecently assaulting his eight-year-old victim in the presbytery and his office on four separate occasions.

The Brisbane District Court heard Colbourne told the child her parents would not get into heaven if she told anyone what he had done.

He also threatened to prevent her mother from converting to Catholicism and to tell her stepfather, who beat her, that she had stolen a book.

Prosecutor Vicki Loury QC said the victim was 14 years old when she finally told her mother what happened, but was not believed.

Colbourne was charged by police in May 2016 after the woman reported to the Royal Commission into Institutional Response into Child Sexual Abuse.

The court heard Colbourne still had inappropriate fantasies but remained on guard to act against them in addition to his limiting age and solitary lifestyle.

The 75-year-old was removed from public functions in 1997 and lives in "virtual isolation" at a Capuchin friary in Melbourne.

Defence barrister Stephen Zillman said Colbourne greatly missed the contact and support of parishioners but accepted that loss was his own doing.

"He's suffered a complete fall from grace," Mr Zillman said.

Judge Tony Moynihan said Colbourne had shown remorse and empathy for his victim and felt a deep loss since leaving the church.

He also noted a jail sentence would be more onerous for the ageing offender despite being his relatively good health.

Colbourne was sentenced to a total 18 months in jail, which will be suspended for three years after he has spent four months behind bars.