Photosynthetic bacteria, Rhodospirillum rubrum, have been reported to change their metabolic patterns depend-ing on the light condition. The genetic approach for such a metabolic change is one of main subject in pho-tosynthetic bacteria. It has been reported that the extrachromosomal plasmid might be related to this metabolic regulation. In this study, we have determined the partial sequences of R. rubrum plasmid pKYl with HindIII fragments and the predicted pKYl ORFs and physical map. We found the 8 putative proteins related to the genetic recombination of bacterium, which is reported to the alternative gene expression. Our results suggest that the genes located in pKYl are possibly involved in the metabolic switch according to the photocondition.