The effects of the height of packed bed in a downcomer on the liquid mixing time in a bubble column with a draft tube are experimentally investigated, while varying gas flow rate and packed bed height under conditions of two types of gas dispersion; gas dispersed into the inner section of the draft tube, and into the annular section between the column and the draft tube. In either type of gas dispersion, the liquid mixing time in the presence of the packed bed increases with increasing superficial gas velocity and decreases with increasing packed bed height. It shows that the degree of increase in liquid mixing times is proportional to the superficial gas velocity raised to the power of 1/3 and the packed bed height raised to the power of 1/4, regardless of the type of gas dispersion.