Bottom sediments and invertebrate benthic faunas were recovered by dredge sampling at four stations off the Tassha coast of Sado Island in the Japan Sea. Nineteen crustacean and 144 molluscan species were found in the bottom sediments. Among the decapod crustaceans, Australeremus triserratus (Ortmann) was identified for the first time in the Japan Sea. The following nine molluscan species were newly found around Sado Island: Emarginula fragilis Yokoyama, Nodiscala matajiroi Kuroda, Pyreneola semipicta (Sowerby III), Dimiya filipina Bartsch, Spondylus barbatus Reeve, Agatha lepidula Habe, Cycladicama semiasperoides (Nomura), Abrina lunella (Gould) and Pitar japonicum Kuroda and Kawamoto. The grain size analysis revealed that the bottom sediments were classified into two groups: coarse-grained sand at shallower nearshore sites and fine-grained sand at a deeper offshore site. The cluster analysis for the molluscan faunas was concordant to the grain size classification of the sediments.