Summary. The aim of this study was to create and optimize matrix sustained  release systems, containing  Diclofenac Sodium. Developed matrix systems were based on НРМС К4М, НРМС К15М and Kollidon^® SR (BASF) as matrix carriers separately, or in combination with other excipients. Throughout the course of the study of swelling kinetics of matrix carriers, it was established that Kollidon^® SR swells in much lower degree than matrices based on НРМС. Temperature, as a factor in itself did not significantly affect the degree of swelling of the matrix based on Kollidon^® SR, but the influence of temperature on the degree of swelling of matrices based on HPMC was not more substantial. Throughout the course of the study, it was established that Kollidon^® SR (nonionogenic, pH independent and swelling in much lower degree matrix) was not effective enough when used separately for the sustained release of  Diclofenac Sodium. Matrices based on HPMC proved more suitable to control the kinetics of release of Diclofenac Sodium. More precise control of the kinetics of release of Diclofenac Sodium can be achieved by adding hydrophilic excipients. Models based on combinations of НРМС К4М, НРМС К15М with Lactosa can be considered as optimal models.