Seth Green

Milo (voice)

Joan Cusack

Mom (voice)

Dan Fogler

Gribble (voice)

Breckin Meyer

Alien (voice)

Elisabeth Harnois

Ki (voice)

Tom Everett Scott

Milo's Dad (voice)

Mindy Sterling

Supervisor (voice)

Raymond Ochoa

Martian Hatchling (voice)

Robert Ochoa

Martian Hatchling (voice)

Ryan Ochoa

Martian Hatchling (voice)

Amber Gainey Meade

Martian

Dee Bradley Baker

Two Cats (uncredited)

Jacquie Barnbrook

Martian

Kevin Cahoon

Wingnut

Matthew Henerson

Martian

Stephen Kearin

Martian