Abstract: The olfactory response of Trigonotylus caelestialium, to rice, Oryza sativa L., and two species of gramineous weeds, Poa annua and Digitaria ciliaris, was investigated with an olfactometer to clarify the role of host-plant odours as olfactory cues in their host-finding behaviour. Third-instar nymphs and adult males were significantly attracted to whole plants (above ground parts) of P. annua. However, adult females were not significantly attracted to whole plants of P. annua. Attractancy of rice to T. caelestialium differed with the growth stage and part of the plant. Adult females were significantly attracted to stems and leaves in the panicle-formation stage, and panicles in the flowering stage. They were not attracted to stems and leaves in the fourth-leaf stage and flowering stage, or to panicles in the milk-and full-ripe stages. Although adult males were significantly attracted to stems and leaves in the panicle-formation stage, they were not attracted to the other rice structures tested. Both females and males were significantly attracted to stems and leaves, as well as panicles of D. ciliaris in the flowering stage. The findings suggest that T. caelestialium use host-plant volatiles as olfactory cues to find their host plants and their invasion to paddy fields were caused by olfactory responses to rice plant.