The dynamic process or structural studies of adsorption and desorption phenomena on the fluid interface has not been clearly established because of its difficulties in experimental instrumentation. In this work, we focused on the bubble coalescence phenomenon, which is known to be strongly affected by trace impurities such as 1 ppm or smaller. We measured the time course of the scattered He-Ne laser intensity irradiated at the contact surface of two bubbles, and the bubble coalescence time was determined in an aqueous solution of n-butanol with concentrations of 5.0, 7.5, and 10.0 mol/m(3). The butanol concentration was so dilute that surface tension was little affected. At each butanol concentration, the bubble coalescence time varied with bubble age, which is the elapsed time from the formation of a bubble. The coalescence time quickly increased in a few seconds since its formation. After that, it gradually increased till the age of a few hundreds seconds, and then suddenly increased again. The initial value of the bubble coalescence time at the bubble age of zero could not be determined because of the difficulty in experiment, however, the value just after the first increase clearly depended on the butanol concentration. The bubble age at the onset of the second sudden increase also clearly depended on the butanol concentration. The slope between the first and the second sudden increase was larger for the higher butanol concentration. The dependence of the bubble coalescence time on the bubble age obtained in this work can be a help to elucidate the dynamic process of adsorption and desorption at the interface.