Abstract: In a trickle bed with gas and Liquid cocurrently flowing downward, chemical absorption with pseudo-first order reaction in the liquid phase was carried out, using air-CO_2-NaOH system. The effective gas-liquid interracial area and average dispersedbubble diameter for pulse flow were determined. The relationships between interracial area and dispersed-bubble diameter, between inteffacial area and flow rates of gas and liquid were obtained. Experiments show that the dispersed-bubble diameter determines the magnitude of effective interracial area. So the rate of mass transfer can be intensified by reducing the particle diameter and increasing the gas and liquid velocity.