Which movie has the best selling soundtrack?

The best-selling soundtrack of all time is "Thriller" by Michael Jackson. Released in 1982, the album has sold over 100 million copies worldwide, making it the best-selling album of all time. The soundtrack features some of Jackson's most iconic songs, including "Thriller," "Billie Jean," and "Beat It." The album also won a record-breaking eight Grammy Awards, including Album of the Year.