Some sacoglossan molluscs, including several species of Elysiidae, are known to incorporate algal chloroplasts, and the incorporated chloroplasts are functional for days to months, depending on species. This incorporation and maintenance of foreign chloroplasts are known as kleptoplasty. In this article, we surveyed photosynthetic activity of several sacoglossans collected in Japan, by analysis of in vivo chlorophyll fluorescence. Our survey found 8 new species that have active chlorophylls, judged by the parameter Fv/Fm, an indicative of the functionality of photosystem II. Identified sacoglossans with active chlorophylls belong to the Bosella, Costasiella, Elysia, Julia, Placida, Stiliger, and Thuridilla genera. Our results strongly suggest that these species possess kleptoplasts. Possession of chloroplasts was confirmed for one of the identified sacoglossans, Elysia trisinuata, by transmission electron microscopy.