Roy Barcroft
— The Purple Monster
James Craven
— Dr. Cygnus Layton
Dennis Moore
— Craig Foster
Linda Stirling
— Sheila Layton
Bud Geary
— Hodge Garrett
Joe Whitehead
— Stewart
Fred Howard
— Prof. Crandal
Rosemonde James
— Helen
Mary Moore
— Marcia
John Davidson
— Emperor of Mars
Wheaton Chambers
— Prof. Benjamin