A countercurrent scrubber was studied to investigate the effects of liquid viscosities on the gas?liquid mass transfer characteristics and flow behavior through cold model experiments by using the dissolved oxygen technique and pressure sensors. The results showed that the effect of viscosity on mass transfer was not merely monotonically increasing or decreasing. However, desorption rates under the condition of median viscosity of the washing liquid presented maximum. Within the investigated viscosity range, the increase of the viscosity (?=1.15 mm2/s) led to the instability of the gas?liquid interface and promoted its surface renewal, which made the turbulence of gas and liquid intensely. When the liquid viscosity (?=1.30 mm2/s) continued to increase, the viscous dissipation effect could not be neglected and then the deformation ability of droplets was weak and not easy to break up, so the performance of mass transfer was poor. At the same time, in addition to the foam flow pattern (QA/QT=0.4?0.6) in the scrubber, the annular flow pattern (QA/QT=1.2?1.5) also showed quite desirable mass transfer performance. Furthermore, when the liquid kinematic viscosity ?=1.00?1.30 mm2/s, the variation tendency of the pressure under different axial-tangential volume flow ratios was similar to the change of the desorption rates under the same liquid flow rate. A flow pattern for good mass transfer also closely related to a high-pressure value. Based on the experimental results, the empirical correlations both for the desorption rate and the pressure drop were given combining with the parameters of flow behavior, mass transfer and operation. The calculated and the measured results agreed well respectively, which can be used for engineering design purpose.