The chromosomes of thirty species of Japanese weevils (Curculionidae) belonging to twelve subfamilies were studied in germ cells. Data on the species investigated and their chromosome numbers together with the sex-determining mechanism are summarized in Table 1. The number of chromosomes shows a variation ranging from 11 to 23. The species showing the haploid number of 11 are numerous being 36.8per cent in frequency. Generally most species of the same genus have a similar chromosome number. All the species under the study reported in this paper are characterized by an X-Y sex-determining mechanism in males.