A new approach to bubble column scale-up based on the quality of mixedness derived from the information entropy concept is presented. Using a step response method for studying mixing in the liquid phase, the carbon dioxide tracer concentrations absorbed in deionized water in a bubble column of 0.289 m in ID have been measured by an electrical conductivity probe under steady flow conditions. The superficial gas velocity was set at 0.0178 m s(-1), 0.8305 m s(-1) and 0.0381 m s(-1) (bubbly flow regime) under clear liquid heights of 0.56 m and 1.84 m, respectively. Following an original algorithm based on the stepwise change of the measured tracer concentrations with time in respective pertinently divided beds, a quality of mixedness concept has been evaluated for the above mentioned operating conditions. It is found that the change of quantity with introduced dimensionless time in this study does not depend on the superficial gas velocity and clear liquid height. The authors argue that for the case of physical absorption of carbon dioxide in deionized water in the bubbly flow regime, the quality of mixedness is dominated by mass transfer from the bubbles to the surrounding liquid and in turn to turbulent mixing on the scale of a mean bubble diameter, which is associated with the liquid transported in the wakes of the rising bubbles. In the present study, the dimensionless quality of mixedness can be related distinctly to a dimensionless time which is defined as the elapsed time divided by the contact time (the Sauter-mean bubble diameter divided by the bubble rise velocity) based on the classical penetration theory. The derived relationship provides significant new information about bubble column scale-up. In addition, a comparison between the quality of mixedness in the upper and lower sections has been illustrated.