Daigo Kashino, 33, was rushed to the hospital and later died.
The actor was in a rehearsal session at a studio in Koto, Tokyo, when he was pierced in the abdomen "with a sword-like object" during an action scene, a police representative told CNN.
The other actors reportedly heard him groan and turned to discover him hunched over -- but no one saw what happened.
Police are now investigating whether his death was an accident or a criminal act.
It marks the second time in recent weeks that a performer has died during a production. Earlier this month, Italian actor Raphael Schumacher was declared clinically dead after he was choked in a stage hanging scene that went wrong.
Swords on stage
Samurai actors perform sword fights at the Toei Kyoto Studio Park.
Sword-swinging "jidaigeki" dramas are an integral part of Japanese culture on stage and in television and film.
The powerful mystique of the samurai sword
Literally translated as "period dramas," they portray the daily lives of samurai, farmers, ninjas, merchants and craftsmen during Japan's Edo period between 1603 and 1868.
Once a national pastime, the genre has now become a bit more niche. One of the biggest studios in the field, Toei, had recently teamed up with Google Japan to boost the art form's dwindling popularity among the younger generation.
Real samurai towns you can visit
Whether the leading character is a samurai or a commoner, the story lines always climax in a swashbuckling sword fight, where the hero comes out victorious.
