The gregarious assassin bug, Agriosphodrus dohrni (Signoret), is widely distributed in East Asia including Japan, and its cooperative hunting often occurs at the young nymphal stage. It has a single generation per year in Japan, and adult emergence occurs in spring, when the adult bugs start mating. This study aims to clarify their behavioral mating process to confirm sex pheromone involvement. Male mating behavior consisted of following four steps: (1: approach) sweeping the antennae intermittently with walking (2: abdomen movement) approaching a female along with rhythmically moving the abdomen up and down (3: mounting) mounting the female by jumping or crawling, and (4: copulation) then inserting his genitalia along a dorsolateral position in relation to the female. Copulation usually succeeded in adult pairs of 16-days-old, but often failed when the adult pairs were 14-days-old or less. These observations suggest that mating success might depend on the sexual maturity of the adults. We also confirmed a capsule-shaped glass rod treated with the female extract functioned as a model to evoke the male sweeping, approaching, and mounting behavior. This glass model facilitates assessment of sex pheromone activity in various chromatographic fractions.