The mark-recapture method was used for 9 coexisting spp. in Kanagawa (Oct., 1981-1984). In the 4 paddy fields studied. S. parvulum, S. eroticum and S. darwinianum (in 2 fields) were dominant resp. in downstream direction. Mating occurred mainly in the morning, and the flying activities decreased during the afternoon. 5. parvulum and S. eroticum covered short distances during a day, while S. darwinianum. S. frequens and S. baccha had low recapture rates, suggesting larger flight distances. In the hills, the community structure was more complex than in the paddy fields, though the population density was lower, and no mating behaviour occurred there. Consequently, the hills are considered to represent the Sympetrum roosting area. The paddy fields community structure in Oct. depended on the extent of the available habitats.