Obi‑Wan Kenobi fights Darth Vader in several key Star Wars screen stories, but the movie most people mean is Star Wars: Episode IV – A New Hope (1977), where old Ben Kenobi duels Darth Vader on the Death Star and is struck down.

If you’re thinking of other famous duels between them, they are:

  • Star Wars: Episode III – Revenge of the Sith – Obi‑Wan fights Anakin Skywalker as he turns into Darth Vader on Mustafar.
  • Star Wars: Episode IV – A New Hope – their rematch years later, as Vader and “old Ben” on the Death Star.

Newer content like the Obi‑Wan Kenobi Disney+ series also shows rematches between them, but that’s a TV series, not a movie.