The 37-year-old actor said in an Instagram post Thursday that Ledger introduced him to new music while filming the 1999 movie 10 Things I Hate About You.
"Heath turned me on to a lot of great music during that summer we worked together," Gordon-Levitt captioned a still from the film.
"I remember the first time I ever heard Radiohead's OK Computer was when I was riding in the back of his car. #tbt," he wrote, referencing Radiohead's critically-acclaimed 1997 album.
Gordon-Levitt and Ledger played Cameron James and Patrick Verona in 10 Things I Hate About You, which co-starred Julia Stiles. Gordon-Levitt previously shared a throwback photo with Ledger, Stiles and Laria Oleynik on set.
"I remember that day :) #tbt," he wrote.
Ledger died of an accidental drug overdose at age 28 in January 2008. Maggie Gyllenhaal, who starred with Ledger in The Dark Knight, praised the star's acting ability in an interview with Watch What Happens Live this month.
"To be amazing like Heath was in a movie that's got explosions and huge stunt scenes and big sets is a whole other thing," the actress said. "I don't know if anyone's ever, ever done that as well as he did in The Dark Knight."
"It was like, 'Whoa, okay. You're on a whole other level,'" she added.