The distribution of gas holdup, the rise velocity of gas bubble swarm and the Sauter mean bubble size are estimated with a small diameter laboratory scale bubble column using electrical resistance tomography (ERT). The theory of gas disengagement based on ERT methods has been developed for estimations of bubble size and bubble rise velocity. The gas holdups of large bubble swarm and small bubble swarm, the distribution of both bubble size are derived through the analysis of gas disengagement based on the differences of the rise velocity of bubble swarm at the cross-section imaged by electrical resistance tomography. Experimental results are in very good agreement with correlations and conventional estimation obtained using pressure transmitter methods. The proposed methodology can be also used as an analysis tool for quantifying and optimizing the performance of other types of complex reaction systems.