The liquid mixing time of a bubble column with a draft tube is experimentally studied. The diameter and height of the column, the diameter and length of the draft tube, and the mode of sparging gas were changed and the liquid mixing time was measured. The lengths of bottom and top clearances have significant effects on the liquid mixing time. The liquid mixing time increases with increasing column aspect ratio of height to diameter, The liquid mixing time of the bubble column with a draft tube is longer than that of a standard bubble column when the column aspect ratio is relatively high. The liquid mixing time has a minimum when the diameter ratio of draft tube to column is 0.5 to 0.6, These effects of equipment dimensions are expressed by an equation. In the experiment using different solutions, the liquid mixing time becomes shorter with increasing liquid surface tension, or with increasing liquid viscosity.