The lipid and fatty acid compositions were affected by growth temperature in Rhodopseudomonas sphaeroides S. The cells grown at 15℃ had lipids in higher content than those grown at 30℃and 40℃. In the former cells the highest lipid class was phosphatidylcholine. In the latter cells, mono- and diglucosyldiacylglycerol and diphosphatidylglycerol were newly produced as minor components in addition to common major lipids. The growth temperature-dependent variations of fatty acids occurred in both unsaturation and chain length. On shifting down temperature a rapid conversion of lipid and fatty acid compositions took place, but on shifting up temperature the conversion was at a slower rate and incomplete. Electron microscopic observation indicated that a variation in the cell structure could be induced with the growth temperature.