A rubber composition having improved processability and which provides a vulcanized rubber exhibiting excellent wear resistance and good tensile strength to service temperatures of up to about 150.degree. C. The composition comprises (1) a crosslinked polymer particle having as repeat units (a) up to about 25% of a conjugated diene unit, (b) at least 70% of an aromatic vinyl unit, (c) about 15% to about 30% of a crosslinking monomer, and (d) about 0.1 to about 30% of a monomer unit having one polymerizable unsaturated group and at least one functional group; and, (2) a non-crosslinked host polymer comprised of at least one member of the group consisting of a polymer having only conjugated diene repeat units, a polymer having repeat units of a conjugated diene unit and an aromatic vinyl unit, a polymer having repeat units of a conjugated diene unit and an .alpha.-.beta.-unsaturated nitrile unit, an acrylic rubber, a polymer having repeat units of an ethylene unit, and polymers having repeat units having functional groups able to interact with a functional group of the functionalized monomer.