A group of young aspiring samurai, all highly serious and idealistic, meet Sanjuro, an older samurai.

His appearance shocks them. He is dirty, unkempt and sloppy, and his manners at times the very opposite of the clean-cut, honourable image of a samurai. The contrast between the spick-and-span boy samurai and Sanjuro - a real samurai - is both amusing and incongruous, and one of the film's themes is this very incongruity. During the course of their association, the younger samurai gradually learn to respect the wisdom and experience of the older man.

As in many of Kurosawa's films, the central subject is that of illusion versus reality (cf. Judo Saga); things as they seem, things as they are, and the muddle that comes from confusing them.