For an improved understanding of liquid-liquid contactor with agitation, it is very important to accumulate data about the droplet size distribution at all locations in the stirred tank. However, there are few methods to precisely and rapidly measure droplet diameter in the tank. In particular, no reliable method has been developed yet to apply to high droplet concentration, which is often utilized in industry. In this study, a real-time high speed image processing system, which was originally developed by the authors, is utilized as the measuring technique for droplet size distribution. The authors improved the experimental apparatus for droplet size measurement, and investigated the conditions with no coalescence and breakup of the sampled droplet. It was shown that various droplet diameter distributions, in some liquid-liquid systems where physical properties were different, were able to be measured. It took less than 0.7 s with error less than 6 % to perform each run, in which about 500 droplets were measured. The dependency of droplet size distribution and specific surface area on impeller revolutional rate, sampling location and droplet concentration were precisely measured. It is also shown that this image processing system is able to detect droplets in a droplet.