The producer, real name Lukas Gottwald, sued the "Tik Tok" singer over the claims, and Manhattan Supreme Court Justice Jennifer Schecter has ruled Kesha's actions amounted to "defamation per se," reported the New York Post.
"There is no evidence whatsoever that Gottwald raped Katy Perry. Moreover, publication of a false statement to even one person, here Lady Gaga, is sufficient to impose liability," the judge wrote.
However, Kesha's legal team said in a statement the singer planned to fight the ruling.
"Judge Schecter issued rulings today on motions for summary judgment in the Dr. Luke litigation," they said, reported Variety. "We disagree with the Court's rulings. We plan to immediately appeal."
Kesha previously sued Dr. Luke for alleged sexual and emotional abuse. She has since dropped her case against him.
She was also ordered to pay Dr. Luke over $373,000 in interest because she was late in her payment of $1.3 million in royalties to the producer.
Dr. Luke worked with the star on her first two albums, "Animal" and "Warrior", and she remains signed to his label, Kemosabe Records, through which she released her latest record, "High Road", last week.