Particle image velocimetry (PIV) was used to measure local bubble size distributions (BSD), gas-liquid interfacial areas and gas holdups in an up-flow ejector, based on the water-air system with different liquid and gas flow rates under the presence/absence of the swirl body. The results show that the bubble flow patterns are different whether to add the swirl body into the nozzle, especially at low gas flow rate because the bubbles formed bubble chain in the ejector with swirl. The mean bubble sizes D-32 of the two are both related to the pressure drop between import and export, gas ratio and liquid flow. The interfacial area and D-32 are both mainly dependent on the local gas holdups. The mean bubble sizes in the absence of swirl body are smaller than that in the presence of swirl under different operating conditions. The gas holdups and interfacial area are larger with swirl than those without swirl. With the increase of the gas fraction, the differences of D-32, a(t) and e(G) become smaller. (C) 2010 Elsevier Ltd. All rights reserved.