Limited hydrolysis of the extruded soy protein concentrate with Protamex (Novo Nordisk A/S), would allow one to obtain new products with desirable functional properties. Response surface methodology which was used to determine optimal conditions of the process showed that the product with the best functional properties can be obtained by conducting the proteolysis at 50^oC with the content of soy protein in the reaction mixture at the level of ca. 70 g/kg, enzyme addition 1.8x10^-2 Anson Units/g protein, as well as pH 6.8 and time of 90 min, which leads to a degree of hydrolysis reaching 8.5%. From the SDS-PAGE electrophoresis of the optimal hydrolysate it follows that proteolysis of extruded material shows more pronounced reduction of 7S than 11S subunits, and an increase in low molecular weight peptides at the bottom of the gel can be observed. Peptides soluble in trifluoroacetic acid aquenous solution (1:1000) were additionally analysed using WP RP-18 HPLC technique. Relative fluorescence measurements and chemical analyses show that Protamex action on extruded soy protein concentrate leads to an increase in surface hydrophobicity and disulphide bonds concentration and a decrease in total and available sulphydryl groups.