Abstract: The invention concerns a biologically degradable polymeric composition containing 5 to 95 wt % of polyhy droxyalkanoate and 95 to 5 wt % of polylactic acid or lactide with addition of 2 to 67 parts of plasticizer or mixture of plasticizers per 100 parts of the polymeric blend. The invention covers also composition containing 0.05 to 5 wt % of a reactive additive. Plasticizers are selected from chemicals, such as esters of citric acid, esters of glycerol, esters of phosphoric acid, esters of sebacic acid and other liquid organic low-molecular polyesters. The reactive additive is selected from a group of chemicals such as acrylic polymers, epoxidized acrylic polymers, diisocyanates and their derivatives, epoxidized oils, oligomeric copolymers of various monomers with glycidyl methacrylate and other species.