Izuku is a teenage boy with green eyes and messy dark green hair, many people believe his hair might be black, but the messiness casts a shadow on his own hair.

During his time at Aldera Junior High, he wore a black gakuran uniform with yellow buttons. At U.A., he wears the standard male uniform: a light grey suit over a white dress shirt and dark green dress pants, along with a red necktie. Izuku usually wears his signature red sneakers for footwear.

His hero costume also undergoes many changes throughout the series, although the basic design stays roughly the same: a green color scheme with highlights, a mask, white gloves, and his trademark red shoes. As he evolves as a hero, the costume gains new additions and changes, with the green steadily growing darker to reflect his growing maturity and competence as a hero. By the final arc, his costume Zeta consists of a dark green attire with gold highlights, redesigned Air Force gloves and Mid-Gauntlets, red belt, blue kneepads, his old damaged respirator, and Gran Torino's cape used as a scarf in place of his old All Might-like cowl.

Though he was initially very skinny, Izuku has gained toned muscles after his ten months of extensive training with All Might, and as the series progresses, these are shown to become more developed and defined as he gradually grows stronger. As his first year at U.A. continues, he attains a highly defined and lean build that helps his emphasis on speed.

After exceeding his One for All limit too many times, Izuku gains scars all over his right arm. He later receives a large burn scar from Dabi.