Pretreatment process of silica-coated PET fabrics, a major low-grade PET waste, was developed using the reaction with NaOH solution. By destroying the structure of silica coating layer, impurities such as silica and pigment dyes could be removed. The removal of impurity was confirmed by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). The pretreated PET fabric samples were used for depolymerization into its monomer, bis(2-hydroxylethyl) terephthalate (BHET), by glycolysis with ethylene glycol (EG), and zinc acetate (ZnAc) catalyst. The quality of BHET was confirmed by DSC, TGA, HPLC and NMR analyses. The highest BHET yield of 89.23% was obtained from pretreated PET fabrics, while glycolysis with raw PET fabric yielded 85.43%. The BHET yield from untreated silica-coated PET fabrics was 60.39%. The pretreatment process enhances the monomer yield by the removal of impurity and also improves the quality of the monomer.