Gas transport characteristics of new polyimide (PI) containing hydroxyl groups in the diamine moiety for seven permanent gases have been investigated: H(2), He, O(2), N(2), CO, CO(2), and CH(4). Changes in the gas separation properties of polyimide during its physical aging over a year have been experimentally revealed. It has been shown that a slow decrease in the permeability coefficients of H(2), He, and O(2) in the polyimide physical aging process and a sharp decrease in those of N(2), CO, CO(2), and CH(4) lead to an exponential increase in the selectivity of gas separation and a displacement of values in the permeability-selectivity plot beyond the upper limit in the case of the O(2)/N(2) gas pair.