Dual-tip conductivity probe is used to determine distributions of rising and descending bubble size in gas-liquid and gas-liquid-solid bubble column. The column is 100 mm in internal diameter and 1500 mm in height. The solid particles used are glass beads with average diameter of 17.82 mu m representing typical particle size for catalytic slurry reactors. Bubbles are categorized to two size classes, small bubbles with chord length (d(c)) less than 10mm and large bubbles with chord length greater than 10 mm. The effects of superficial gas velocity (1.0 cm/s <= U-g <= 6.4 cm/s), solid holdup (0% <= epsilon(s) <= 30%) and radial location (r/R = 0, 0.4 and 0.7) on bubble size distributions are determined. A fundamental statistic test-chi(2)-test is used to test whether the experimental rising and descending bubble size distributions follow the commonly used distributions. it is found that increasing Ug and E, can increase the size and quantity of large bubbles. The results indicate that most small rising bubble size distributions are well characterized by lognormal or gamma distributions at low solid holdup. The descending bubble size does not follow any often used distributions; the majority of them are less than 4 mm, and a few of large descending bubbles appear with the increasing of s. and U.. Usually, the total bubble size distributions are not fit for the lognormal distributions except when the descending bubbles are few under the condition of U-g = 1.0 cm/s and epsilon(s) = 0%. (c) 2008 Published by Elsevier B.V. on behalf of The Institution of Chemical Engineers.