Abstract: A bis(trisubstitutedtrimellitic anhydride) derivative and a polyesterimide for optical communications, the polyesterimide being formed therefrom. The polyesterimide has a high refractive index, so that when using such polyesterimide as a material for a core of an optical fiber, the range of materials that can be selected for the cladding becomes wide. Also, a coating property and adhesion to a substrate are improved, thereby providing a good film forming property and thermal stability. Also, because the polyesterimide can minimize optical loss at a near infrared wavelength range, the polyesterimide is very useful as an optical material in the optical communications field adopting the light of near infrared wavelength.