It's thought the front of the rollercoaster broke away from the rest of the train when it was travelling through a tunnel.
The ride takes visitors to the theme park through a twisting and turning landscape inspired by the Wild West.
The train travels past mineshafts, waterfalls and caverns.
The man who died is thought to be in his 20s or 30s.
Statement
The injured people are aged nine to 47, according to reports.
A top Disney official, Michael Eisner, made a statement following the accident.
He said "our hearts and prayers go out to those injured and to the family of the deceased."
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