We experimentally investigated the effect of organic substrates on growth of Spirulina platensis in heterotrophic culture. Organic substrates added to SOT medium were sugars, organic acids and amino acids. The specific growth rate of S. platensis is heighest in the medium with added glucose, but S. platensis did not grow well in the medium with added polysaccharides. In the medium with added alpha-ketoglutarate, succinate or fumarate, the specific growth rate of S. platensis was negative. The metabolic path was estimated from the experimental results.