The composition dependence of the phase-separated structures in the polymer mixtures consisting of a thermotropic liquid crystalline (LC) copolyester (X-7G) and poly(ethylene terephthalate) (PET) was investigated by means of polarized light microscopy. For this purpose the mixtures were solution-cast into thin films, followed by isothermal annealing at 270 degrees C. Although the final structure was the LC droplets dispersed in the isotropic matrix for all mixtures, a variety of pattern-forming processes were observed; depending on the composition. For the mixtures with higher X-7G content, dewetting of the X-7G component on the surface of the glass substrate played an important role in the pattern formation.