Since 2003 mixed martial arts(MMA) gained international exposure and widespread publicity in Korea. Criminal responsibility for accidential death which occurs in MMA was reserched in this paper. The Point of this reserch is ob this case can correspond to the negligent homicide at business or not. Ob the person like a chief manager of company which hold mma game, referee, ring doctor, ring second, player has performed his duty of care which was demand by the law is key issue. If they have taken any proper and prompt action to prevent player from danger of death when they foresee accidential death negligence at business have to be recognized. Beacause mma is more dangerous than any sport, severe duty of care is provided for Officials of mma. Therefore must Officials of mma give attention to their business.