Although the film was not a huge success upon release, it has amassed a large fan base over the years.

In a steampunk version of England, James Ray Steam is sent a mysterious spherical device that his father and grandfather accidentally discovered while searching for a new energy source for England's steam engines. James is increasingly hounded by members of the opposing O'Hara Foundation and discovers the Foundation's sinister aims. He is also confronted by Scarlett O'Hara St Johns, the granddaughter of the chairman of the O'Hara Foundation, who seems to like him.

Steamboy was Katsuhiro Otomo's first feature film after Akira (1988). Originally intended as three 40-minute original video animation episodes, Steamboy remained in production for ten years and at the time was the most expensive Japanese animated film ever produced.