In the present work, for expression and evaluation of characteristics of the drop size distribution, we propose the indices of representative diameter, Ds*, sharpness, Ss* and skewness, Sa.We investigated the drop size distributions with varying dispersed phase concentrations and impeller speeds as stirred operation condition factors in various impeller stirred tanks using a real-time high-speed image processing system, which was developed by ourselves. From the drop Size distribution obtained, we discuss quantitatively the characteristics of the drop size distribution in various impeller stirred tanks with three defined indices. As a result, it is found that the defined indices can express and be used to evaluate more accurately the drop size distribution over a wide range of dispersed phase concentrations and impeller speeds. It is also found that three-dimensional plots showing the dependence of the defined indices on the dispersed phase concentration and the impeller speed as stirred operation condition factors can express and be used to evaluate the characteristics of the liquid-liquid dispersion conditions in each stirred tank. Furthermore it is found that the relationship between the defined indices and the dispersed phase concentration for constant power consumption per volume can be used to discuss the quality of performance of the liquid-liquid dispersions in various impeller stirred tanks.