Axial mixing is an important factor which affects gas and liquid (G-L) mass transfer in monolith channels significantly and therefore monolith reactors design and operation.Monolith reactor bed consists of a great number of straight channels in parallel which are separated by very thin walls.Due to the special structure, G-L distribution is formed at the monolith entrance and keeps the distribution into channels through whole bed height without G-L redistribution.So the effect of liquid distributor on G-L distribution is critical to axial mixing in monolith bed.In the present work the axial-mixing behanvior of the liquid phase in cocurrent down flow under the two types of liquid distributors (nozzle and glass beads distributor), square channel monoliths of different sizes (100, and 400 cells per square inch or cpsi) has been studied by analyzing the residence time distribution (RTD) of the injected tracer pulse.