A sadistic sexual predator's appeal against his indefinite jail term imposed for two decades of terror has been rejected.

Alan Neil Rosewarn, of Taranaki, was last year sentenced to preventive detention for abusing two women and their children.

The indefinite term was imposed in the High Court at New Plymouth and means despite Rosewarn becoming eligible for parole after 10 years, he may never be released.

He admitted charges including rape, sexual violation, kidnapping, threatening to kill and child cruelty.

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Rosewarn appealed against the preventive detention on the basis a minimum term would be sufficient punishment.

But in a judgment delivered today, the Court of Appeal disagreed.

"There is nothing in the matters raised by the appellant that alter the careful evaluation undertaking by the [sentencing] judge," the judgment says.

Rosewarn's offending with the first woman was between 1990 and 2007. He was in his mid-20s and she was much younger than him.

The sentencing judge said he had "emotionally taken control of her and had alienated her from her family and friends".

Rosewarn subjected the woman to "devastating emotionally, physical and sexual abuse, which escalated as time passed".

He would beat her, throw her into walls, punch her face and pull her hair out, among other "indignities" and "cruelties".

When she was pregnant, Rosewarn would jump on her if she fell to the ground as he beat her.

Rosewarn also beat the woman's children, including throwing a newborn around a car seat.

In 2009, he served a separate jail sentence for the offending.

His old abusive ways continued with a second woman beginning in 2008.

The woman's child wasn't spared either. They had a milk bottle thrown at their face and Rosewarn would lock them in a car without food or water.

NZME je mb