After popular groups such as Creedence Clearwater Revival earned his Berkeley-based label, Fantasy Records, a fortune during the 1960s, Zaentz made an auspicious entry into feature film production with One Flew Over the Cuckoo's Nest (1975). Starring Jack Nicholson and based on Ken Kesey's underground classic, the film became one of the biggest—and least likely—critical and commercial smashes of the day, earning a best picture Oscar for Zaentz and co-producer Michael Douglas. Zaentz's subsequent efforts, often literary adaptations, have usually been worth the wait, particularly Amadeus (1984), another Oscar champion, and The Unbearable Lightness of Being (1988), which introduced Lena Olin to American audiences. The Saul Zaentz Company Film Center, a post-production sound facility, opened its doors in the early 80s.

Als film producent werkte hij aan de navolgende films 1975 One Flew Over the Cuckoo's Nest 1977 Three Warriors 1978 The Lord of the Rings 1984 Amadeus 1986 The Mosquito Coast executive producer 1988 The Unbearable Lightness of Being 1991 At Play in the Fields of the Lord