A method is provided for estimating durability of an optical member against pulsed excimer laser beam irradiation. The method includes the steps of (a) irradiating a test sample for the optical member with a pulsed excimer laser beam to induce changes in transparency of the test sample with respect to the pulsed excimer laser beam, the irradiation being performed for such a time period as to cover not only a linear region and a saturation region and (b) measuring changes in the transparency of the test sample with respect to the pulsed excimer laser beam as a function of the cumulative number of the excimer laser pulses that have irradiated the test sample in step (a). The method further includes the step of (c) repeating steps (a) and (b) with a plurality of different first predetermined energy densities of the pulsed excimer laser beam to derive a correlation equation representing the changes in the transparency of the test sample in the linear region and the saturated region in terms of the energy density of the pulsed excimer laser beam and the cumulative number of the excimer laser pulses and (d) estimating the durability of the optical member under actual usage conditions using the derived correlation equation.