Generally speaking, Japanese doctors need to study for at least four years. Although most professional doctors in Japan need to study for four years, only medical doctors need to study for four years, so it is difficult for them to become Japanese doctors. Generally, it takes four years for a doctor of science and engineering, and four to five years for a doctor of arts. Generally speaking, Japanese doctors need to study for at least four years. Although most professional doctors in Japan need to study for four years, only medical doctors need to study for four years, so it is difficult for them to become Japanese doctors. Generally, it takes four years for a doctor of science and engineering, and four to five years for a doctor of arts.