In this paper, a method is described that makes easier application of Chang's method for the determination of molecular weight of copolymers by GPC. Determinations of molecular weight of EP-copolymers have been performed with this method. The values of the resultant weight- and number-average molecular weight are rather close to the experimental data, and the values of intrinsic viscosity [η]care close to the values measured with Ubbelodhe viscometers [η]d.