The mating behavior of Monochamus alternatus was observed in glass containers and on pine trees in a field cage. The male was initially passive, staying motionless with his antennae widespread while the female was actively moving in his vicinity. Courtship was initiated by the female approach toward the male. The male then dashed and mounted her and she began walking with him on top. The male licked to calm female and succeeded in copulating when she stopped walking. A long pair-bond was formed in which repeated copulations occurred with the ovipositing female. Adults of both sexes copulated with several mates. Taking over of a mate from a pair was done by both male and female. The antennae were used to ward off disturbing males or females. The presence of a male sex pheromone was supposed to be the attractant for mate searching. Antennae and body odor were also supposed to play a role in mate recognition and initiation of courship. The mating behavior was explained in terms of the fitness theory and reproductive success.