Microalgae utilize carbon dioxide (CO₂) and bicarbonate (HCO3-) as carbon sources through CO₂ concentrating mechanism. In this study, we demonstrated the relationship between the extent of chemotactic response towards HCO3- and CO₂ fixation efficiency of the wild-type and mutants of Chlamydomonas reinhardtii CC125 in a microfluidic device. The movement of the microalgae was quantitatively evaluated by the degree of skewness and asymmetry of distribution. The results showed that the well-growing mutants had a tendency towards higher HCO3- concentration. In addition, the correlations between the chemotactic response and both the growth (△OD) and the photosynthetic efficiency (Y(II)) showed high linearities. This result implies that chemotaxis can be used as a strategy for high-throughput screening to identify microalgal strains with high CO₂ fixation efficiency.