To date, a large number of methods for producing nanomaterials have been developed. Previously, we have described technologies for synthesizing CdS and ZnS semiconductor compounds with nanoparticles in a polymer matrix using a solvothe1mal method [1, 2]. It is known that polymer structures ar·e networks in which each element can be regarded as a nanoreactor [3]. The pa1ticle size of the material synthesized in it will be detennined by the size of the nanoreactor. In this study, we report on the results of synthesis of cadmium and zinc sulfides in BMA copolymer with styrene using cadmium stearate (C11H3sCOO)2Cd, zinc stear·ate (C11H3sCOO)2Zn, and thiourea (CS(NH2)2. The precursors were dissolved in benzene and air-dried to the complete removal of the solvent. The resulting material was placed in a glass cell and heated in the air at a temperature of 120-180°C for 20-25 min. Examination of the optical absmption and photoluminescence spectra of the composites obtained at T = 130-150°C has revealed that the specti·a are shifted to shorter wavelengths compar·ed to the single-crystal cadmium and zinc sulfides. A similar· effect of blue shift is caused by the fo1mation of nanoparticles in the studied material. In te1ms of a simple quantum chemical model, the average particle size was estimated by the fo1mula: (8µ· M)l/2 where µ is the reduced mass of the exciton and Mis the sho1t-wave shift value. The average size of the nanopa1ticles did not exceed 6-7 mn. Synthesis at higher temperatures (T> 150°C) led to a change in the optical prope1ties of the composites. This experimental fact is atti·ibuted to the ti·ansition of the copolymer in the state of viscous flow [3], which leads to the breaking of the nanoreactor walls and to the coalescence of the nanoparticles into lar·ger entities.