Recently we isolated the purple photosynthetic bacterium, Rhodopseudomonas sp. Rits, which was phylogenetically related to Rhodopseudomonas (Rps.) palustris. In this study, the light-dependent and time-dependent changes in the carotenoid composition were investigated by HPLC analysis of extracts from the cultures. All seven carotenoids in the biosynthetic pathway from lycopene to spirilloxanthin were detected. Especially, 3,4-didehydrorhodopin, having twelve conjugated double bonds as well as one terminal hydroxy group, was isolated in a remarkably large amount and fully characterized for the first time. The biosynthetic intermediate was commonly found in the Rps. palustris strains (CGA009, Morita and NBRC100419).