Abstract: Mass transfer rates of n- and i-butanol into single water drops falling through continuous phases of these liquids have been measured using Colburn and Welch technique. The results, after having been corrected for end effects and expressed as dispersed-phase mass transfer coefficients as well as a correlation factor R, have been compared with the Kronig and Brink model and with some selected data published in literature. From the results obtained it seems reasonable to conclude that the Kronig and Brink model will apply to circulating drops up to a drop Reynolds number of 50 or 60, which is similar to the conclusion reached recently by Treybal after careful examination of Johnsons paper, and will fail to remain valid above 80. The data are generally in agreement with those given by Johnson et. al. on single drops but somewhat higher than those of Heertjis et. al. in spray towers. The i-butanol-H2O system is found to show larger deviations all the way from the theoretical values than the n-butanol-H2O system. In as much as no interfacial turbulence has been observed by Schlieren technique in both cases, the difference in mass transfer rates between two systems can only be attributed to the difference in drop behaviour caused by the difference in such properties as viscosity and interfacial tension, and shape of drops. The variation of drop terminal velocities with drop sizes has also been examined. The results are found to be lower than those predicted by the correlation of Hu and Kintner for drops without mass transfer, but they are similar in trends in that the terminal velocities show also a maximum value at a certain transition drop diameter of about 3.5mm (this is in fair agreement with the calculated values of 3.5 and 3.8 mm for n- and i-butanol, respectively). It is thus likely that the Kronig and Brink model could apply to these systems up to such a drop size, above which the results would appear to approach a model descri bing the behaviour of oscillating drops such as that of Handles and Baron.