The medical applications of photosynthetic bacteria are summarized. Photosynthetic bacteria can produce various types of physiological active substance such as vitamin B,,, ubiquinone (coenzyme Q10), 5-aminolevulinic acid (ALA), porphyrins and RNA. In particular, photosynthetic bacterial ALA was commercially applied to cancer diagnosis and treatment. Recently, ALA has been applied to the treatment of acne vulgaris and the suppression of the inflammatory response to coronary and iliac injuries. In addition, the recent applications of RNA from a marine photosynthetic bacterium as a medical supplement for immune improvement and suppression of infection are described. Furthermore, the feasible application of a biopolymer consisting of RNA from a photosynthetic bacterium as a drug delivery system (DDS) to cancer treatment is described.