The film by director Paolo Sorrentino beat Belgium's The Broken Circle Breakdown, Denmark's The Hunt, Cambodia's The Missing Picture and Omar from Palestine.
"Thank you to Roma and to Napoli," Sorrentino said.
The film had already won numerous international awards, including a Golden Globe, and is a tribute to the great Italian master Federico Fellini and his muse Rome, the Eternal City.
Italy is no stranger to the Oscar stage. The nation's films have won 11 Academy Awards, most recently in 1998 for Life is Beautiful.
Watch a video of Sorrentino's acceptance speech: