The gas-liquid mass transfer occurring in Taylor flows right after the bubble formation stage were investigated in a flow-focusing microreactor. The colorimetric technique proposed by Dietrich el. al. (2013) was used for locally visualizing and characterizing the gas-liquid mass transfer. Thanks to this method, the liquid-side mass transfer coefficients k(L), were measured at the moment right after the bubble is detaching from the gas film near the cross-junction of the microreactor. Experiments were carried out for several flow conditions (95.7 < Re < 226.1, 0.0043 < Ca < 0.010, 0.4 < We < 2.3, Bo = 0.044) and bubble size (2.34 < L-b/l< 5.59). The results have demonstrated that the contribution of mass transfer right after the bubble formation stage is reasonably larger to those obtained at the bubble flowing-stage. (C) 2016 Elsevier Ltd. All rights reserved.