Here we developed new baffled flasks for stable and efficient gas-liquid mass transfer in small-scale aerobic microbial fermentation. For this purpose, various types of baffled flasks were designed, fabricated using 3D printer, and evaluated in terms of mass transfer performance and cell mass production. To investigate the mass transfer efficiency of gas according to the baffle type, three types of flasks with latticed-, curved- or swirled-baffles on the bottom were prepared. An experimental result of CO 2 absorption in alkaline water in three types of baffled flasks indicated that latticed-baffled flask had the best mass transfer performance. The gas transfer rate was also observed to have a strong influence on the productivity of microbial cultures. When E. coli cells were cultivated for 6 h, the baffled flask with higher mass transfer rate yielded higher cell and lower acetate concentration. When correlated with the result of E. coli culture, the CO 2 mass transfer performance, which is expressed in reciprocal of CO 2 dissolution time, showed a linear relationship with the final cell concentration. In the newly done study, based on the cell concentration, the latticed-baffled flask with pentagon and hexagon was found to have 30.4% and 6.1% higher culture performance in terms ...