The growth responses of Spirulina platensis NIES-46, a brackishwater strain originally isolated from Lake Texcoco Mexico, to some physico-chemical factors and nutrients were investigated. The optimum conditions for growth were the following: light intensity of 160 µE m^-2 sec^-1, temperature of 30°C, pH 10, and chlorinity of 0.55‰. NIES-46 strain could utilize both inorganic and organic phosphorus sources. Values on the different growth parameters for orthophosphate and other organic phosphorus sources were as followings: half-saturation constant of 0.02-0.07 mg-P/l; maximum growth rate of 0.8-1.0/d; minimum cell quota of 0.08-0.32 pg-P/cell, and level for saturated growth yield of 0.3-1.0 mg-P/l. The result that this species utilized effectively a rather wide range of both inorganic and organic phosphorus and showed a high growth rate suggests that mass production of this species is possible by recycling organic waste.