In an 89-page ruling, the three-judge panel unanimously found the That '70s Show actor had failed to demonstrate the lower court made errors that would warrant granting him a new trial.
The panel also rejected a petition filed by Masterson that claimed ineffective assistance of counsel.
Masterson's first trial ended with a deadlocked jury in 2022, but at his retrial the following year, he was convicted of raping two women. He was sentenced to 30 years to life in prison.
His lawyers said in a statement they would seek review at the California Supreme Court.
Among the claims the court rejected were Masterson's convictions violated the 10-year statute of limitations for forcible rape, as the statute does not apply where there are multiple victims; the trial court excluded evidence in his favour; and the trial court exhibited bias against his religion.
Masterson is a prominent member of the Church of Scientology, and his accusers are former members who said they grew disillusioned with the institution after they were assaulted.
They said church officials told them what had happened to them was not rape, and that its policies prevented them from going to police.
The church vehemently denied having any such policy.
Masterson, 50, has been serving his sentence at the California Men's Colony in San Luis Obispo. He will not be eligible for parole for more than 20 years.
Masterson starred with Ashton Kutcher, Mila Kunis and Topher Grace in That '70s Show from 1998 until 2006. He had reunited with Kutcher on the 2016 Netflix comedy The Ranch, but he was written out of the show after the allegations surfaced.
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