We study the effectiveness of adding of mesomorphic polyesters into polyarylated sulfone matrix. This method purposed to obtain unidirectional ribbon-like prepregs and fiberglass plastics on their basis. We study the change of viscosity of the polymers and its positive influence on the factors of technological effectiveness and porosity of the material. Physical-mechanical and thermal properties of the fiberglass plastics practically do not depend on the concentration of mesomorphic polymers. We discover a synergism. The strength of composites under shear increases (up to 25%) in the case of adding of 2-5% of the mesomorphic polymers into the polyarylated sulfone matrix. A mechanism of this phenomenon is not clarified, yet.