Damage by thrips is a problem during the cultivation of open-field chrysanthemum. We investigated the species composition and seasonal abundance of thrips on open-field chrysanthemum and surrounding weeds over the course of a year. On open-field chrysanthemum, Thrips nigropilosus Uzel, T. tabaci Lindeman, and Frankliniella occidentalis Pergande were dominant. The dominance of T. tabaci in May and that of T. nigropilosus from September to October was the same on both chrysanthemum and weeds. In addition, four species of thrips were identified on the mother stocks of chrysanthemum and weeds from December to February. Therefore, continuous weeding from May to October and from December to February may affect the density of thrips on open-field chrysanthemum.