We have performed a first principles study of structural, electronic, and optical properties of rhombohedral Sb 2Te 3 and Bi 2Te 3 compounds using the density functional theory within the local density approximation. The lattice parameters, bulk modulus, and its pressure derivatives of these compounds have been obtained. The linear photon-energy dependent dielectric functions and some optical properties such as the energy-loss function, the effective number of valance electrons and the effective optical dielectric constant are calculated and presented in the study © 2012 IEEE.