Effects of the gas velocity and the ratios of outer/inner column diameter on the values of local gas holdup in a double tube bubble column were experimentally studied. The local gas holdup in the annular section was measured by means of a conductivity probe technique. The maximum value in the radial profile of gas holdup and the mean gas holdup increased with increasing superficial gas velocity, while they were hardly affected by the ratios of outer/inner column diameter within the range of the present experiment. Based on the velocity profile of fluid in laminar flow, modeling the gas holdup profile in the annular section was carried out. The results calculated by the experimental equation agreed well with the measured data for the radial profiles of the gas holdup.