Agitation power were measured in agitated vessels with highly viscous liquids under conditions of aeration and non-aeration. The agitation power data obtained in the absence of aeration were empirically correlated by the use of two traditional parameters, i.e., power number and Reynolds number. The agitation power required under aeration were also correlated based on the consideration of the relationship between the power and the shape of the cavity formed behind the impeller blade. Apparent volumetric mass transfer coefficients were measured with the assumption that the liquids in the vessels remained in a state of the perfect mixing. In the region where the agitation power is relatively great, the relationship between the mass transfer coefficient and the agitation power could be shown by straight lines in log-log plots. In this region, a simple correlation equation was proposed for the mass transfer coefficient. In the region where agitation power is not so great, on the other hand, the mass transfer coefficients were shown to be estimated well by the use of the above-mentioned correlation equation and the correlation equation proposed, for bubble columns (Tokanai et al., 2001).