A three-judge panel from the California's 2nd District Court of Appeal unanimously issued the decision.
"We are disappointed by today's decision and respectfully disagree with the Court of Appeal's conclusions regarding the fairness of Mr. Weinstein's trial," Weinstein spokesperson Juda Engelmayer said in an email. "At the same time, the court correctly recognized that his sentence cannot stand."
The decision came a day after prosecutors in New York decided Weinstein would not face a fourth trial there, dropping the #MeToo-era case on Thursday after the accuser said she could not bear to testify again.
The former movie magnate still stands convicted of another sexual felony in New York, and he remains behind bars. But the New York rape charge had remained unresolved after an overturned conviction followed by two hung juries.
In California, Weinstein, 74, was convicted in December 2022 of one count of rape and two counts of sexual assault against an Italian model and actor known during the trial as Jane Doe 1. Weinstein was sentenced to 16 years in prison.
The former movie magnate's lawyers argued in his appeal that in his Los Angeles County trial, the testimony of the head of a film festival was unfairly limited by Superior Court Judge Lisa B. Lench, and had been seeking a new trial.
In New York, Weinstein is awaiting a September sentencing on his still-standing assault conviction involving a different woman. Prosecutors are seeking a 20-year prison term. He would serve his California sentence only after that.
After the Los Angeles trial, Jane Doe 1 later came forward under her name, Evgeniya Chernyshova, when she sued Weinstein in civil court.
The Associated Press does not typically name people who say they have been sexually abused unless they come forward publicly as Chernyshova did. Her attorney also said she consented to being named.
Chernyshova testified that Weinstein arrived uninvited to her hotel room during the 2013 LA Italia Film Festival and assaulted her.
Weinstein's defense argued that a judge wrongly prevented his trial lawyers from asking about Facebook messages between Chernyshova and festival head Pascal Vicedomini that would have shown they had a sexual relationship.
The questioning would have shown she perjured herself when she said she and Vicedomini were just friends and colleagues, Weinstein's lawyers argued. And they said it would have bolstered their argument that she was not even in her room on the night of the alleged assault.
"The lower court all but gutted Mr. Weinstein's defense," attorney Jennifer Bonjean told the appeals judges at April 23 oral arguments.
David Glassman, who represented the state, said any affair was irrelevant. "It doesn't apply to any contested issue in the case," he said.
Before his sentencing, Weinstein told the judge that this was a "made-up story" from a woman he had never met.
The Los Angeles trial jury acquitted Weinstein of the sexual battery of a massage therapist and failed to reach verdicts on counts involving two other women.
"This is not the end of the appellate process," Engelmayer said in his email Friday. "We intend to seek review in the California Supreme Court because we continue to believe significant legal errors affected the proceedings and warrant further review."
Emails seeking comment from Chernyshova's attorney and the Los Angeles prosecutors were not immediately answered.