The man, aged in his 60s, was sentenced in the County Court this month after pleading guilty to one charge of persistent sexual abuse of a child under 16.

"Sexual abuse of young children is abhorrent, and a clear message must be sent that people who seek to engage in such conduct will face significant terms of imprisonment," Judge Trevor Wraight said.

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The charge to which the man pleaded guilty encompassed seven specific incidents of sexual abuse committed against the girl, who was aged under 10.

The court heard that on one occasion, the offender instructed the victim not to tell anyone, or he would get in trouble.

"The victim wanted to tell someone, but did not want you to get mad at her," Judge Wraight said.

On another occasion, the victim kicked out at the perpetrator and told him to leave her alone.

He laughed and she replied, "It's not funny", before going into another room.

The court heard the man came in and said, "[I've] been a very naughty person lately".

He told the girl he would not do it again, but the victim replied, "You've said that before".

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It was alleged the man also committed other "sexual misconduct", which was detailed to the court for context.

The matter was reported to police after the victim told her parents.

The offender admitted to police that he had sexually abused the girl.

He said he had known it was wrong, but kept doing it.

Judge Wraight said the sexual offending against children under the care of adults was very serious.

"As such, when offending of this nature occurs, it is rightly described as, quote, 'inherently evil and depraved, violating the basic norms of civilised behaviour, and striking at the value the community places on the lives and wellbeing of the young'," Judge Wraight said, referring to remarks made in another case.

He said this man's offending was also a "serious breach of trust".

"The victim would attend your home in order to enjoy a normal relationship between granddaughter and grandfather. Instead, in the trust of that relationship, you sexually abused her on a number of occasions," Judge Wraight said.

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The judge noted victim impact statements in which the girl's mother said she felt guilty for not being able to protect her daughter, and the girl's brother worried about his sister and parents.

A forensic psychologist assessed the man's risk of reoffending in such a way as "low to moderate", and reported the man had expressed regret and remorse.

Judge Wraight accepted the offender had demonstrated genuine remorse and acknowledged the need to undertake treatment.

He said the man's early plea of guilty also carried significant weight.

Judge Wraight declared the man had to serve at least four years of his six-and-a-half year sentence before he would become eligible for parole.

The offender will be a registered sex offender for life.

Had he not pleaded guilty and been found so, Judge Wraight would have imposed a sentence of eight years, with a non-parole period of five and a half years.

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