The effects of physico-chemical factors and nutrients on the growth responses of Spirulina platensis isolated from Lake Kojima (K-2 strain) were determined. The optimum conditions for growth were the following: ligh intensity of 2,500-10,000 lx, pH 6.5-9.0, 30 to 35°C temperature and 0-7.6‰ of chlorinity. S. platensis (K-2 strain) requires no vitamins for growth essentially. However, growth enhancement was observed with vitamin B₁₂ among the B-group witamins tested. Likewise, hormones such as kinetin and giberellin exhibited stumulatory effect on growth. The alga could utilize inorganic and organic phosphorus sources. Values on the different growth parameters for orthophosphate, β-glycerophosphate, adenosine diphosphate, and phos phocreatine were comparatively similar; half-saturation constant, maximum growth rate, minimum cell quota and level for saturated growth yield were about 0.01-0.02 mg P/ℓ, 0.8/day, 0.1-0.2 pg P/cell, and 0.4-0.7 mg P/ℓ, respectively.