This invention relates to a rubber composition having a high storage modulus (G′) and a low loss tangent (tan δ), and more particularly to a rubber composition comprising 2 to 60 parts by mass of a low-molecular weight aromatic vinyl compound-conjugated diene compound copolymer (B) having an aromatic vinyl compound content of 5 to 80% by mass, a vinyl bond content in a conjugated diene compound portion of 5 to 80% by mass, a weight average molecular weight as measured through a gel permeation chromatography and converted to polystyrene of 5,000 to 500,000 and at least one functional group based on 100 parts by mass of a rubber component (A) composed of at least one of natural rubber and synthetic diene-based rubbers.