To produce the subject composition having improved hysteresis characteristics by compounding a diene polymer modified with an alkoxysilane derivative with a specific organosilane compound and a carbon black as a reinforcing filler.

(A) A diene polymer functioned or modified with an alkoxysilane derivative (e.g. propyltrimethoxysilane) is compounded with (B) a reinforcing filler consisting of carbon black or a mixture of carbon black and silica (preferably highly dispersible precipitated silica) and further with (C) an organosilane compound having amine or imine functional group and expressed by the formula (Z is a primary amine functional group, an imine functional group, etc.; R1 to R3 are each a 1-12C alkyl, an aryl, etc.; (n) is 0-2) (e.g. aminopropyltrimethoxysilane). The diene polymer of the component A is preferably butadiene-styrene copolymer, etc. The amounts of the components B and C are preferably 30-100 pts.wt. and 0.1-10 pts.wt. based on 100 pts.wt. of the component A, respectively.