Feedpipe backmixing in an agitated vessel could be detected successfully using a newly developed conductivity technique. The idea of this technique is to use the difference in the conductivity between tap water in the feedpipe and NaCl solution in the vessel. When the vessel fluid penetrates into the feedpipe due to high agitator speed, the conductivity around the electrodes in the feedpipe is increased. The change in the conductivity was sensed by the electrodes and the resultant output signal was recorded by a pen-chart recorder. In order to get maximum sensitivity in detecting the conductivity change, an electric circuit was modeled by considering current-voltage relations of the circuit. When the minimum measurable peak occurred on the recorder by feedpipe backmixing, the NaCl concentration change around the electrodes was on the order of 10_-5mole/1. Compared to the 40 mmo1/1 concentration of NaCl in the vessel, this resolution was comparable to the 1,000 times dilution of the vessel concentration.