Saitama is an ordinary-looking bald man with brown eyes, a thin but well-built physique, and is of average height and weight. He used to have a full head of short black hair but lost it due to the intensity of his hero training regimen.

Saitama is revealed to have sharp facial features, fearsome eyes, and chiseled musculature. His posture changes as well, with a slack posture and sloping shoulders when lax, and a straightened posture and squared shoulders when serious.