For a diffused waveguide with a Gaussian profile the index profile is given approximately by a polynomial function. Using the result derived by Ikuno, an approximate solution of the propagation constants for guided modes is obtained. It is shown that the propagation constants obtained by our approach are in agreement with the results obtained by ray technique, better than those obtained by the earlier approach corresponding to secant hyperbolic profile. The equation is simple for calculation and particularly, the deyiations in high order modes are decreased considerably.