Carbon dioxide emission, which acts as one of the major agents of greenhouse gases (GHG), has significant effects on global warming. Nowadays, there is a considerable global tendency toward decreasing the amount of GHG emissions to the atmosphere. In the present study, a simulated power plant flue gas (Be’sat, Power Plant, Tehran) with a constant injection rate of 21.41 cm3 s−1, including 10% CO2, 7% O2 and 83% N2 , was injected to the Synechococcus elongatus culture under two different light–dark (L/D) cycles: 24-0 and 16-8. Additionally, the biomass productivity and the CO2 biofixation rate by microorganisms were investigated. The highest biomass productivities were recorded as 0.68 and 0.52 g L−1 d−1 for 24-0 and 16-8 L/D cycles, respectively. Furthermore, the maximum rate of the CO2 biofixation was 1.26 g L−1 d−1 for the 24-0 L/D cycle and 0.98 g L−1 d−1 for the 16-8 L/D cycle during the cultivation.