NOVELTY - A rubber composition comprises ethylene-( alpha )-olefin and non-conjugated polyene copolymer (A), silicon hydride-containing compound (B) (II) having two silicon hydride groups in one molecule and silicon hydride-containing compound (C) (III) having three silicon hydride groups in one molecule. The ethylene-( alpha )-olefin and non-conjugated polyene copolymer is a copolymer of ethylene, ( alpha )-olefin and non-conjugated polyene. The ( alpha )-olefin has 3-20 carbon atoms. The weight ratio of ethylene unit with respect to ( alpha )-olefin unit is 35/65-95/5.    USE - Rubber composition is used for fuel cell sealing material for fuel cell, and hard-disk-drive top cover gasket, gasketing for liquid injection molding for hard-disk drive, and wire-connector sealing material for wire connector such as electric wire connector for motor vehicles (all claimed).    ADVANTAGE - The rubber composition provides molded product having excellent sealing performance, heat resistance, acid resistance, mechanical characteristics and outgas-proof property.    DETAILED DESCRIPTION - A rubber composition comprises ethylene-( alpha )-olefin and non-conjugated polyene copolymer (A), silicon hydride-containing compound (B) of formula (II) having two silicon hydride groups in one molecule and silicon hydride-containing compound (C) of formula (III) having three silicon hydride groups in one molecule. The ethylene-( alpha )-olefin and non-conjugated polyene copolymer is a copolymer of ethylene, ( alpha )-olefin and non-conjugated polyene. The ( alpha )-olefin has 3-20 carbon atoms. The weight ratio of ethylene unit with respect to ( alpha )-olefin unit is 35/65-95/5. The iodine number of ethylene-( alpha )-olefin and non-conjugated polyene copolymer is 0.5-50. The intrinsic viscosity of ethylene-( alpha )-olefin and non-conjugated polyene copolymer in decalin solution at 135 degrees C is 0.01-5 dl/g.    R3,R5=1-10C monovalent group and optionally substituted saturated hydrogen group or aromatic hydrocarbon group;    a,b=0-20;    R4=1-30C bivalent organic group or oxygen;and    R6=1-30C trivalent organic group.