The study of using new materials for the production of optical sensors, synthetic vision systems, and modern glasses with specified frequency polarization properties is impossible without their experimental research. Such research is focused on the further solution for the problems of synthesis or optimization of the technological process using accurate data on the parameters of a specific sample of production optical material. Here are the results of measurements and algorithms for processing the data obtained in order to estimate the refractive index of zinc selenide single crystals of the same ZnSe CVD type from different batches. A method for determining the refractive index is developed based on the spectrophotometric method using the reflection and transmittance spectra of plates, as well as the spectrum of the reflection from the sample surface. The results of the study showed not only the correctness of the proposed method. They also showed that in the studied part of the infrared range, the obtained refractive indices for different samples of zinc selenide from the same batch differ more from each other than indicated in reference publications. It should be taken into account when developing products of transmittance optics.