A photosynthetic bacterium strain P17 having high growth rate and assimilating ability of organic acids was isolated from several soil samples, which was identified as Rhodospirillum rubrum. Cultural conditions of the strain P17 were examined for the production of starter culture used in the treatment of organic waste water. The addition of organic acids mixture as carbon source containing 0.2% Na-acetate, 0.1% Na-propionate and 0.2%r Na-lactate and 0.1% of yeast extract as growth factor stimulated the cell growth. The maximal cell production was obtained at 30℃, pH 7.0, 2,500 lux of illumination and 50∼100 rpm of agitation. Under the optimal conditions of batch and fed-batch culture systems in a Jar fermentor, 5.17 g/ℓ and 7.93 g/ℓ of cells were obtained after 5 days of cultivation, respectively. In continuous culture system, the cell productivity was 0.206 g/ℓ/h at a dilution rate of 0.21 h^(-1). When R. rubrum P17 was cultivated in a soybean curd waste water, initial COD level(3,240 ㎎/ℓ) of the waste water was reduced to 250 ㎎/ℓ after 4 days of cultivation.