Growth kinetics and cultivation technique ofSpirulina platensiswere studied by using 1 liter Roux‐flask. Optimum temperature and pH forSpirulina platensisunder continuous illumination of white fluorescent light were found to be 30°C and 9.5 respectively. In the logarithmic growth phase, growth followed Monod's equation; the maximum specific growth rate,μm, and saturation constant,KL, were 2.0 day‐1and 9.2 klux respectively. During the linear growth phase, it followed the equation:dX/dt=μmln(1+I0/KL)/ah1, whereI0is the growth limiting factor. Growth yield of the algae ranged 0.01–0.02 g‐cell/kcal. Photosynthesis efficiency ranged 6–12%. Growth was inhibited asPo2in the gaseous phase increased to 95%. An automatic controller for pH of culture medium was devised with the feeding of CO2gas. Such an automatic operation promoted the algae productivity (4.5 g dry wt./l) and also improved the medium utilization.