Abstract: The requirement of much longer duration of startup is an important characteristic of a close-boiling fractionating column, and consequently the search for ways to shorten this period have been received much concern and attention. The conventional method of starting up a column is under the condition of constant vapor velocity, while in this paper, the authors propose another way of operation, i. e. startup with stepwise lowering of vapor velocity. The mathematical models of those two methods of startup are developed and solved to obtain the analytical solutions of exponential type to represent the change of concentration profile. The derived equations are in agreement with the experimental data. Both theoretical study and experimental work show that, when the same final concentration is reached, the duration of startup required for proposed operation is less than that for the conventional. This result may have some significance to the operation a close-boiling fractionating or batch distillating column.