Bis--hydroxyethyl terephthalate having an optical density measured in a 10 wt % methanol solution at a measurement wavelength of 380 nm and a cell optical path length of 10 mm of 0.000 to 0.006. The present invention makes it clear that purified BHET having an optical density of 0.006 or less provides high-quality PET having excellent purity, whiteness and transparency.