The axial and radial profiles of the gas holdup and bubble parameters in an external-loop airlift reactor of inner diameter 0.09 m and height 1.8 m were measured with the differential pressure method and dual-tip electrical conductivity probe at different superficial gas velocities.Air and water were used as the gas and liquid phases，respectively.The experimental data of the average and local gas holdups，bubble size and its distribution，bubble rising velocity，bubble frequency and gas-liquid interfacial area were obtained，and were analyzed based on the gas-liquid flow field and bubble-bubble interaction.The local gas holdup was correlated in terms of superficial gas velocity，axial height and radial position based on the experimental data.