Drop size distribution(DSD)or mean droplet size(d32)and liquid holdup are two key parameters in a liquid-liquid extraction process.Understanding and accurately predicting those parameters are of great importance in the optimal design of extraction columns as well as mixer-settlers.In this paper,the method of built-in endo-scopic probe combined with pulse laser was adopted to measure the droplet size in liquid-liquid dispersions with a pump-impeller in a rectangular mixer.The dispersion law of droplets with holdup range 1％to 24％in batch pro-cess and larger flow ratio range 1/5 to 5/1 in continuous process was studied.Under the batch operation condi-tion,the DSD abided by log-normal distribution.With the increase of impeller speed or decrease of dispersed phase holdup,the d32 decreased.In addition,a prediction model of d32 of kerosene/deionized system was established as d32/D=0.13(1+5.9φ)We-0.6.Under the continuous operation condition,the general model for droplet size prediction of kerosene/water system was presented as d32/D=C3(1+C4φ)We-0.6.For the sur-factant system and extraction system,the prediction models met a general model as d32/D=bφn We-0.6.