The stink bug, Piezodorus hybneri (Heteroptera: Pentatomidae) is an important soybean pest in South Japan. Male-produced pheromone system of P. hybneri has been elucidated as a mixture of three components. However nobody has checked the attractiveness of synthetic pheromone in the field. Recently, we found that P. hybneri was attracted to (E)-2-hexenyl (E)-2-hexenoate, one pheromone component of the bean bug, Riptortus clavatus (Heteroptera: Alydidae) which is also one of the predominant soybean bugs. We evaluated the attractiveness of the pheromone and (E)-2-hexenyl (E)-2-hexenoate in a soybean field. Synthetic P. hybneri pheromone attracted P. hybneri adults in the field. However, attractiveness of synthetic pheromone was less than that of (E)-2-hexenyl (E)-2-hexenoate alone. Though both sexes of adults were attracted to these baits, sex ratio of P. hybneri adults attracted to synthetic pheromone was female-biased, while almost equal numbers of both sexes were attracted to (E)-2-hexenyl (E)-2-hexenoate. These results suggest that attractiveness to P. hybneri may have different functions between P. hybneri pheromone and (E)-2-hexenyl (E)-2-hexenoate. We further discuss the differences of biological functions among these attractants.