The case stems from a 2019 interview with Paris Match magazine, where Polanski allegedly called Charlotte Lewis a liar following her accusations.
The court's ruling did not address the truth of the rape allegation but focused solely on whether Polanski's comments in the interview constituted defamation against Lewis. Polanski denied the charges.
The verdict was delivered on Tuesday afternoon in a Paris court.
Lewis said she felt let down by the verdict and would appeal.
"I feel sad," she said. "For us, it's not over."
Polanski was not in court, and his lawyer Delphine Meillet said the court recognised his right to challenge people who make accusations against him. She noted that the verdict came on the opening day of the Cannes Film Festival, calling it "a symbolic day".
"It's a victory for the rights of the defence," the lawyer said.
At the heart of the accusations was that Polanski rebutted Lewis's allegations of sexual assault in the 2019 interview with Paris Match, describing them as a "heinous lie".
Lewis had contended the remarks were defamatory, launching a legal battle against the 90-year-old director, known for classics such as Rosemary's Baby, Chinatown, and The Pianist.
Lewis, who first made her allegations public in 2010, claimed Polanski "sexually abused me in the worst possible way when I was just 16 years old", referring to an incident in 1983 in Paris during a casting session for his film Pirates.
The filmmaker has faced several other accusations of sexual assault that allegedly occurred over several decades, including a notable case from 1977 where he was charged with the rape of a 13-year-old in the United States. He pleaded guilty but fled to Europe in 1978 before sentencing could take place.