Trypsin was immobilized in quasi-soluble polyanion-polycation complexes with retention of the enzyme activity. The activity of the immobilized enzyme strongly depends on pH of the prepared solution, Composition, relative concentrations and molar masses of the polyelectrolytes. The highest activity of trypsin (about 93%) was found in the case of the complexes Na-poly(styrenesulfonate)-poly (diallyldimethylammonium chloride): trypsin = 10:1, prepared at pH 3.0, with high molar mass of the polyanion (about one million). This method can be proposed for immobilization of various serine proteases.