The correlation between the optical (such as complex refractive index, energy band gap) and thermal (such as diffusivity, effusivity and conductivity) properties of Zn1-xMgxSe (with 0 <= x <= 0.50) crystals are presented. The Zn1-xMgxSe mixed crystals were grown by the modified high-pressure Bridgman method and were studied using spectroscopic ellipsometry as well as photopyroelectric technique. We found that when Mg content in Zn1-xMgxSe increases the value of E-g increases. Moreover, the values of thermal conductivity and refractive index of studied materials decrease with increasing Mg content in Zn1-xMgxSe. Therefore, from the performed measurements, one can conclude that the incorporation of Mg as constituent into ZnSe crystals plays a crucial role in the observed optical and thermal response. (C) 2016 Elsevier B.V. All rights reserved.