In this study, effects of some impurity atoms included in IIIA group such as Al, Ga, and In on the optical properties of the beta-Si3N4 structure have been discussed. The calculations were made using Density Functional Theory (DFT) in 0-15 eV range and local density approximation (LDA) as the exchange-correlation. Using the real and the imaginary parts of the complex dielectric function, the basic optical properties of beta-Si3N4 such as dielectric coefficient, refractive index, absorption, reflection coefficients have been investigated. As a result of the calculations, it is determined that optical properties of structure have been significantly changed with doping. (C) 2017 Elsevier GmbH. All rights reserved.