A method of preparation of purified bacteriophage with increased antibacterial activity, in which from bacterial lysate of phages is obtained, advantageously in the presence of lysozyme, chelating factor and detergent, in a continuous manner with ultrafiltration on membranes, the phage containing high molecular mass preparation, devoid of bacterial cell wall and other contaminants, free of toxins and endotoxins, active in tests of bacterial lysis, which is characterized by chromatography HPLC, In SDS-PAGE electrophoresis, immunoblotting, biological tests of bacterial lysis, and is dedicated for phage therapy of bacterial infections and tumors and for production of phage deriving pharmaceutical preparations.