Systems from ultra high molecular weight polyethylene-high density and urethane elastomer with prevailing concentration of the first component and their basic mechanical and rheological properties have been investigated. It is established that the blends with optimal concentration of urethane elastomer have elongation at break higher than 2000% at monoaxial orientation and flow in melt enough for their processing by conventional methods. Peculiarities in their phase structure are established by DSC- and WAXS investigations. The degree of crystallinity is considerably higher than the additive one. The influence of the component composition and the experimental conditions on the super-additivity of the crystallinity of the thermoplast-elastomer systems is discussed.