Summary Algal cultivation is a potential candidate for CO 2 mitigation. CO 2 plays important roles in mass cultivation of algae, including supplying carbon source and adjusting medium pH . To assess the possibility of using edible cyanobacterium N ostoc flagelliforme as carbon storage device, the growth characteristics of N . flagelliforme batch cultured under elevated CO 2 concentrations (0, 2.5, 5, 20, and 40%) were investigated in this study. Results showed that the net photosynthetic rate, efficiency and carbon sequestration rate at 20% CO 2 were increased at a maximum of 121 μmol O 2 (mg chl a ) −1 h −1 8.40% and 0.17 g CO 2 L −1 day −1 , and increased by 0.42, 1.03 and 1.13 folds compared with that of the control, respectively. Higher CO 2 concentration resulted in the declines in photosynthetic rate, efficiency and carbon sequestration rate because of medium pH reduction. Accordingly, the dry cell weight, amount of exopolysaccharides and protein content of N . flagelliforme cells at 20% CO 2 were obtained at a maximum of 1.45 g L −1 , 54.98 mg L −1 and 57.75%, increased by 0.93, 0.29 and 0.8 folds compared with that of the control, respectively. These results provided important information for CO 2 mitigation by N . flagelliforme and would shed more light on elucidating the mechanisms of CO 2 tolerance in cyanobacterium.