An alkali-tolerant Chlorella sp. AT1 mutant strain was screened by NTG mutagenesis. The strain grew well in pH 6-11 media, and the optimal pH for growth was 10. The CO2 utilization efficiencies of Chlorella sp. AT1 cultured with intermittent 10% CO2 aeration for 10, 20 and 30 min at 3-h intervals were approximately 80, 42 and 30%, respectively. In alkaline medium (pH = 11) with intermittent 10% CO2 aeration for 30 min at 3-, 6- and 12-h intervals, the medium pH gradually changed to 10, and the biomass productivities of Chlorella sp. AT1 were 0.987, 0.848 and 0.710 g L-1 d(-1), respectively. When Chlorella sp. AT1 was aerated with 10% CO2 intermittently for 30 min at 3-h intervals in semi-continuous cultivation for 21 days, the biomass concentration and biomass productivity were 4.35 g L-1 and 0.726 g L-1 d(-1), respectively. Our results show that CO2 utilization efficiency can be markedly increased by intermittent CO2 aeration and alkaline media as a CO2-capturing strategy for alkali-tolerant microalga cultivation.