Emile Hirsch - Speed Racer.
(Joseph Gordon-Levitt, Zac Efron, and Shia LaBeouf were considered for the role)
(Preparing for the role Hirsch watched every Speed Racer episode.  He also talked to NASCAR driver Jimmy Johnson at Lowe’s Motor Speedway)
Nicholas Elia - young Speed Racer
John Goodman - Pops Racer (Speed’s father)
Susan Sarandon - Mom Racer (Speed’s mother)
Christina Ricci - Trixie (Speed’s girlfriend) (Elisha Cuthbert and Kate Mara were considered for the role)
Ariel Winter - young Trixie
Paulie Litt - Spritle (Speed’s younger brother)
Kenzie and Willy (chimpanzees) - Chim Chim (Spritle’s pet) (Two chimpanzees were used to portray Chim Chim)
Scott Porter - Rex Racer (Speed’s older brother)
Matthew Fox - Racer X (Keanu Reeves turned down the role)
Nayo Wallace - Minx (Racer X’s girlfriend)
Hiroyuki Sanada - Mr. Musha (a businessman)
Rain as Taejo Togokahn - a rookie racer (Interesting Fact: Rain made his first Hollywood movie appearance in Speed Racer)
Yu Nan - Horuko Togokahn (Taejo Togokhan’s sister)
Christian Oliver - Snake Oiler
Milka Duno - Gearbox
Benno Fürmann - Inspector Detector
Roger Allam - E.P. Arnold Royalton (corrupt owner of Royalton Industries)
Kick Gurry - Sparky (Speed’s mechanic and best friend)
Richard Roundtree - Ben Burns (a commentator who was formerly a racer)
Melvil Poupaud - a race commentator
Peter Fernandez - a race commentator