Abstract: Bubble size and velocities rising and descending were measured by dualtip conductivity probe in a bubble column reactor, which operated with air and water. The column was 0.1 m in diameter and 1.5 m in height. The superficial gas velocity (ug) was ranged from 0.53 cm/s to 7.46 cm/s. The results indicated that dispersed bubble regime, transition regime and coalesced bubble regime could be observed within the experimental ug where the transition ug among these three regimes were 2.13 cm/s and 4.26　cm/s, respectively. Bubble size and velocity were homogenous in dispersed bubble regime while changed with the changes of axial and radial position in other regimes. With the fixed ug, the descending bubble size was 30%~40% less than that of rising one in the centre of the column and the descending bubble velocity was about 55% less than that of the rising one when the axial height was 0.6 m(h/D=6), while in r/R=0.8(dimensionless radial direction), the descending bubble velocity was about 40% lower than that of the rising one.