The aim of investigation was to develop a system for protein sustained release based on the use of poly(3-hydroxybutyrate) (PHB) microcapsules loaded with bovine serum albumin (BSA).Materials and Methods. To develop microcapsule we used PHB obtained microbiologically by a strain-producer Azotobacter chroococcum 7B. microcapsules loaded with model protein BSA were produced by double emulsion technique "water/oil/water". morphology of microcapsules was investigated by methods of confocal and scanning electron microscopy, when the loading and release of BSA was examined spectrophotometrically. In vivo biocompatibility of microcapsules was studied in accordance with intramuscular implantation and histology findings.Results. The study of BSA incorporation and its sustained release from microcapsules for more than 190 h demonstrated the efficacy of proposed system. The mechanism of protein release was found to occur due to the rupture of polymer walls. moderate tissue response to the implantation of obtained microcapsules was demonstrated.Conclusion. developed PHB microcapsules loaded with BSA are good model of long acting protein drugs.