The mixing characteristics of powdered activated carbon slurry of relatively high concentration was studied to find the optimal mixing condition in an adsorption column with bubble-agitation. System adopted was an activated carbon slurry column with internal looping where the mixing of adsorbents are conducted by gas input. From th experiment, it was found that the mixing rate increased with gas input and decreased with increasing activated carbon content, but the mixing rate increased with increasing activated carbon concentration at the superficial gas velocity of 0.04-0.06m/s. From the analysis of gas holdup and the calculated slurry velocity, this tendency could be explained by the enhanced slurry fluidization due to coalescence of bubbles and the condition of high mixing with activated carbon concentration and input gas velocity could be suggested.