To obtain the subject composition with highly dispersed silica, crosslinkable rapidly, hard to cause scorching, and capable of giving tires with excellent mechanical strength characteristics, high resistance to electrification and good fuel economy, by compounding a polar group-contg. diene-based rubber, silica as a reinforcing agent, a polyether-based polymer, a silane coupling agent and a silylating agent.

This composition comprises (A) a rubber component consisting mainly of a polar group-contg. diene-based rubber, (B) a reinforcing agent (pref. white carbon manufactured by wet process), including silica, (C) a polyether- based polymer, (D) a silane coupling agent, and (E) a silylating agent (pref. phenyltriethoxysilane), wherein the component A is composed pref. of 50-85 wt.% of a conjugated diene monomer unit, 0.1-10 wt.% of a polar group-contg. vinyl monomer unit, and 19.9-44.9 wt.% of an aromatic vinyl monomer unit, and the component C is pref. a copolymer of ethylene oxide or propylene oxide and allyl glycidyl ether.