The experiments were carried out in the fiber-glass ponds in the greenhouse during the months of April, July and September in order to determine the effect of seasonal temperature and light intensity on the blue pigment C-phycocyanin and protein content of Spirulina platensis. While C-phycocyanin content was found higher in Autumn (332.7 ±1 μgmL-1), lower and similar in Spring and Summer (327.5 ±2 and 323.4 ±1 μgmL-1) respectively. The water temperature of Summer, 34.52 ±0.05ºC, was found to be higher than the temperatures of Autumn (30.04 ±0.06) and Spring (24.87 ±0.5 ºC). The light intensity of July (1195.08 ±29 μmol m-2 s-1) was also found to be higher than the light intensity of September and April (822.46±61 and 684.40 ±13 μmol m-2 s-1). The higher protein ratio (r.09 ±1) was found in Autumn in Spirulina bi-omass and lower and similar protein ratios (h.15 ±0.9, f.16 ±0.3) were recorded in Spring and Summer respectively. It was concluded that C-phycocyanin and protein contents of Spirulina platensis cultures were different in April, July and September.