Abstract: Spirulina platensis, cyanobacteria was cultivated in a helical photobioreactor and in a continuous system. Cultivation continued at different salinity ratios (10, 20, 30%) for 10 days. The total volume of the photobioreactor was 24.3 L comprising of 18 L nutrition medium and 6.3 L algae. Each day, the system yielded 10 L of algae and 10 L of nutrition medium was added into the system. At the end of 10 day experiment, the medium reached to1.042x107 filament L-1 from an initial filament density of 7.596x106 filament L-1 at 10% salinity, 7.409x106 filament L-1 from an initial filament density of 7.60x106 filament L-1 at 20% salinity and to 7.381x106 filament L-1 from an initial filament density of 7.62x106 filament L-1 at 30% salinity. Variations in proximate composition of S. platensis occurred due to the different rates of salinity. Carbohydrate, TMS (Total Mineral Substance) and lipid values increased; protein levels decreased in parallel with the increase in salinity. A reduction of approximately 13.05% occurred in the protein values, 26.08% increase in the lipid value, 31.85% increase in TMS and 9.86% increase in carbohydrate values were observed.