Planar optical waveguide fabricated in erbium-doped glasses became attractive due to their light emission at 1.5 m, thereby shown like candidates for optical amplifiers or waveguide lasers. In this study we focused on the influence of chemical compositions of specially formulated Er 3+ and Er 3+ /Yb 3+ -doped silicate glasses on the ion-exchange process and optical properties of the m fabricated waveguides. Optical waveguides were fabricated by a routine K + โ Na + ion-exchange in a set of the glasses that had various contents of the RE ions and different optical basicity. Properties of the fabricated planar waveguides were studied by means of dark mode spectroscopy (DMS) at 671 nm while the chemical composition of the waveguides was determined using electron microscope analysis (EMA). The results are discussed from a point of view of the content of the active ions, glass permeability (i.e. glass covalence and glass basicity) for the exchanged ions and optical properties of the fabricated waveguides. Diffusion that proceeds during the ion-exchange will be characterized by the pertinent diffusion coefficients and concentration depth profiles of the involved ions important for the resultant properties. It was found that presence of the RE could substantially lower the penetrability of the glass matrix for the migrating ions.