Flax (Linum usitatissimum) is an annual plant with a long history of cultivation and a great significance in medicine and industry. To increase the valuable qualities of flax products, the flax genome has been genetically modified, with the specific aims to improve flax properties and usefulness for various industries. Through introduction of polyhydroxybutyrate (PHB) synthesis genes from Ralstonia eutropha into flax genome, biomechanical properties of fiber have been improved. In this paper, we report that those fibers contain higher quantities of phenolics in addition to PHB thus making the modified fibers a very suitable material for biomedical application, provided that the fabric is not treated chemically. The linen PHB-fabric promotes human fibroblast proliferation and has been shown to have antimicrobial activity in the in vitro studies. Based on this quality of the fabric, the new dressing for chronic wounds was developed and proven to be successful in a pre-clinical trial. Therefore, it was demonstrated that modified flax fibers are suitable material for biomedical industry.