This study is focused on the effect of butanol addition on mass transfer and bubble size dispersion in dilute butanol solutions [from 0 to 1% (v/v)], in a split-cylindrical airlift and compared with pure water. Bubble size distribution is measured by photography and picture analysis. Bubble diameter in dilute butanol solutions is about 3.5 times more than it in pure water. Also increasing of butanol concentration leads to decreasing of bubble diameter about 25%. Increasing of gas velocity inlet by increasing of coalescence rate leads to increasing of bubble diameter, so the biggest bubble observed in the highest gas velocity inlet and lowest butanol concentration. Although butanol provides an aditional decrease of mass transfer coefficient, but by reducing bubble diameter, active surface for mass transfer increases that leads to increasing of volumetric mass transfer coefficient. Furthermore, a correlation for volumetric mass transfer coefficient is exhibited using butanol concentrations and gas velocity inlet as independent variables.