Onizuka is of medium height, he has brown eyes, blond hair (dyed) and pierced ears. Onizuka is an avid smoker, he is rarely seen without a cigarette in his mouth. Unlike other anime, where the character's equipment remains unchanged, Onizuki's equipment is constantly changing. He is well known for having a wide variety of costumes.

Onizuka is very athletic: he is able to bench press 150 kg (approximately 330 pounds). He has a second dan black belt and was a college karate champion. In addition, he has stated several times that he follows a daily training regimen that includes 500 push-ups, 1,000 pull-ups and 2,000 squats.