Despite the film's English title, "Godzilla vs. Mechagodzilla II," the film is not a sequel to Godzilla contro i robot (1974). A later film featuring Mechagodzilla was released in western markets as Gojira × Mekagojira (2002). In their original Japanese language, all of these films are differentiated by what word is used for "versus". The original 1974 film uses "tai", this film uses "VS", and the 2002 film uses "X".
The English dub version of the movie is the only movie where Rodan is referred to by his real name, Radon.
Proportional to the film's run-time, this film has the most Godzilla screen-time out of all the films in the franchise (around 20% of the film).
Originally intended to be a remake of Il trionfo di Kong (1962). 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 - Il gigante della foresta (1967), but they feared this would violate Turner's copyright. Toho ultimately decided to use Mechagodzilla, although the Mechani-Kong theme was used in the film.
On the official poster, Mechagodzilla appears with his prototype design, and doesn't look like the robot seen in the movie. This version of Mechagodzilla was meant to split and transform into smaller battle vehicles, a jet fighter and a tank, which can also be seen on the poster.