Despite the film's English title, "Godzilla vs. Mechagodzilla II," the film is not a sequel to Godzilla vs. Mechagodzilla (1974). The film was retitled due to the fact that in the Western world, different films in a series rarely have the same title unless they're remakes. A third film with the same title in Japanese, Godzilla Against MechaGodzilla (2002) ("Godzilla vs. Mechagodzilla"), was also retitled for the Western market (as "Godzilla Against Mechagodzilla".)
Originally intended to be a remake of King Kong vs. Godzilla (1962) a.k.a. King Kong vs. Godzilla. The producers, however, considered Turner Entertainment's asking price for the rights to King Kong too high. They then planned on using Mechani-Kong from King Kong Escapes (1967) a.k.a. King Kong Escapes, but they feared this would violate Turner's copyright. They ultimately decided to remake Godzilla vs. Mechagodzilla (1974) although the Mechani-Kong theme was used in the film.