John Williams' score for the original 1977 Star Wars movie beat off other contenders for the title such as 2001: A Space Odyssey and Close Encounters of the Third Kind.
The poll was conducted by science fiction website Totalscifionline.
The score to Star Trek II: The Wrath of Khan, composed by James Horner, came in second place, while Vangelis' haunting electro soundtrack for Blade Runner - recently voted the best sci-fi movie of all time - completed the top three.
Composer John Williams won an Academy Award, a Golden Globe, a BAFTA Award and a Grammy Award for his work on all six Star Wars movies between 1977 and 2005.
His score for Close Encounters of the Third Kind also made the top 10, coming in at number eight.
Matt McAllister, editor of Totalscifionline, said: "With his score for Star Wars, John Williams created one of the most iconic and unforgettable soundtracks of all time.
"Most people could identify the movie from just a few bars of the main title music and Williams' work across all of the Star Wars movies really does create a palpable sense of intergalactic space battles and galaxy-spanning adventures.
"For many moviegoers, this is now the definitive sound of science fiction."
Top ten sci-fi movie soundtracks/composers:
1 Star Wars (John Williams)
2 Star Trek II: The Wrath of Khan (James Horner)
3 Blade Runner (Vangelis)
4 Star Trek the Motion Picture (Jerry Goldsmith)
5 Flash Gordon (Queen)
6 2001: A Space Odyssey (Richard and Johann Strauss, György Ligeti)
7 The Day the Earth Stood Still (Bernard Herrmann)
8 Close Encounters of the Third Kind (John Williams)
9 Aliens (James Horner)
10 Transformers the Movie (Vince DiCola/Stan Bush)