To mitigate CO2 discharged from thermal power plants, studies on CO2 fixation by the photosynthesis of microalgae using actual exhaust gas have been carried out. The results are as follows. 1. A method is proposed for evaluating the maximum photosynthesis rate in the raceway cultivator using only the algal physical properties; 2. Outdoor cultivation tests taking actual flue gas were performed with no trouble or break throughout 1 yr using the strain collected in the test; 3. The produced microalgae is effective as solid fuel; and 4. The feasibility studies of this system were performed. The system required large land area, but the area is smaller than that required for other biomass systems, such as tree farms.