A new capillary technique, based on electrical conductivity, is developed for the rapid and accurate in situ determination of the bivariate drop-size-concentration distribution for reactive liquid-liquid dispersions. The basic principle of this method is to force drops through a precision bored glass capillary by means of a low-how gear pump, after collecting them in its funnel-shaped entrance. The electrical device is designed to measure drop size and drop concentration by difference of conductivity between dispersed phase and continuous phase as drops transformed into cylindrical slugs pass between two detection points in the capillary. This new technique can give information about the in situ state of a reactive- dispersion and can provide with on-line monitoring and control of the quality of liquid dispersion process.