Modification of petroleum asphalts with polymeric materials was examined. Polymers containing a crystalline phase can be used as modifiers. Based on an adsorption model of the reaction of the polymer with the disperse phase of the asphalt, a relation was obtained for determining the lower concentration of cross-linking of the polymer in the polymer-asphalt composite. It was shown that the total maximum content of asphalt in the polymer and disperse phase should not exceed 25%.