This paper reports results of the authors’ study on community structure, seasonal and annual variations of jellyfishes in Jiaozhou Bay based on 1980 to 1998 investigations data. So far totally 62 species were found, among which 14 species were first recorded in Jiaozhou Bay. Of the 62 species, 56 belong to Hydromedusea, 4 Syphomedusea, and 2 Ctenophora. Most of these Medusea and Ctenophores are low salinity and wide temperature types, a few are high salinity and high temperature types. The dominant species was Obelia in spring were Phialidium, Eirene, Muggiaea atlantica, and Zanclea costata etc. In summer. Jellyfishes could seldom be collected in winter. The species abundance of jellyfish in Jiaozhou Bay was usually highest in June and July and quite high in autumn, but low in winter and spring. Analysis of annual variations showed that jellyfish species abundance decreased dramatically from 80s to 90s.