A new series of thermotmpic random copolyesters were prepared and their thermal and mesomorphic properties were investigated. The copolymers were consisting of triad aromatic ester type mesogens and mixed spacers of disiloxyl and polymethylene groups along the main -chain. The dependence of melting and isotropization transitions on the molecular weight of a copolymer was established using a series of fractionated samples. Differential scanning calorimetry and analysis on a polarizing microscope were the two main research tools employed in this investigation. Optical textures of the polymers did not provide a clear conclusion as to the nature of mesophases formed by the polymers, although they appeared to be poorly organized nematics.