Ultra high cis polybutadiene prepared with a monomeric neodymium catalyst, Nd (neodecanoate) 3·(neodecanoic acid) was used for a series of rubber composites, and their vulcanized properties were analyzed. Ultra high cis polybutadiene exhibited high mechanical and dynamic properties, such as high tensile and abrasion resistance, compared to those of nickel-polybutadiene, which were attributed to the high molecular weight, narrow molecular weight distribution and ultra high cis microstructure. The acrylonitrile-butadiene copolymer worked well in the blend with ultra high cis polybutadiene in terms of the high mechanical properties but not for the dynamic properties, such as the abrasion resistance. In a series of composites of ultra high cis polybutadiene and natural rubber, high tensile properties, tear strength and tan δ (G"/G', hysteresis) were obtained as the content of natural rubber was increased, and abrasion resistance increased with increasing ultra high cis polybutadiene content with a concomitant decrease in tan δ. A simple Maxwell model was introduced to explain the viscoelastic properties of the ultra high cis polybutadiene blends. The elastic properties, e.g. tensile, modulus and rebound properties, were compared with the spring as energy storage, and the viscositic properties, such as heat build-up and abrasion, corresponded to the dashpot as an energy dissipater.