The polar surface of inorganic nanoparticles and the nonpolar surface of a polymer are thermodynamically incompatible. This is the reason for the insufficient improvement of polymer properties by the addition of nanoparticles. Therefore, the technology of UHMWPE bromination is developed in order to create an agent affecting the interphase interaction of nanoparticles with a UHMWPE matrix. In this paper, the results of the use of brominated UHMWPE as an adhesion-changing agent in the case of UHMWPE/boron carbide composite are reported. It has been found that brominated UHMWPE decreases interphase interactions of boron carbide nanoparticles with the UHMWPE matrix and deteriorates the mechanical properties of the composite.