NOVELTY - A rubber composition contains a copolymer (A) of ethylene, 3-20C alpha-olefin and non-conjugated polyene, and silicon hydride group-containing compound (C) (II) having two silicon hydride groups in a molecule. The non-conjugated polyene is one or more types of norbornene compound (I). The weight ratio of ethylene unit with respect to alpha-olefin unit of copolymer (A) is 35/65-95/5. The iodine number and intrinsic viscosity measured in decalin solution at 135degreesC, of the copolymer (A) is 0.5-50 and 0.01-5 dl/g, respectively.    USE - For sealing material for fuel cell, top cover gasket for hard-disk drive, and sealing material for and wire connector (all claimed) for motor vehicle.    ADVANTAGE - The rubber composition provides fuel cell sealing material with excellent mechanical characteristics, sealing-proof property, heat resistance and acid resistance. The hard-disk drive top cover gasket component formed using the rubber composition has low hardness, excellent mechanical characteristic, heat resistance, compression permanent-deformation characteristic and leak-proof property. The wire connector sealing material formed using the rubber composition has excellent outgas-proof property, sealing performance, insertion property of wire and oil bleed proof property.    DETAILED DESCRIPTION - A rubber composition contains a copolymer (A) of ethylene, 3-20C alpha-olefin and non-conjugated polyene, and silicon hydride (SiH) group-containing compound (C) of formula (II) having two SiH groups in a molecule. The non-conjugated polyene is one or more types of norbornene compound of formula (I). The weight ratio of ethylene unit with respect to alpha-olefin unit of copolymer (A) is 35/65-95/5. The iodine number and intrinsic viscosity measured in decalin solution at 135degreesC, of the copolymer (A) is 0.5-50 and 0.01-5 dl/g, respectively.    n=integer of 0-10;    R1=H or 1-10C alkyl;    R2=H or 1-5C alkyl;    R1=1-10C monovalent group, (un)substituted saturated univalent hydrogen group or aromatic hydrogen group;    a,b=integer of 0-20;and    R2=1-30C divalent organic group or oxygen atom.    INDEPENDENT CLAIMS are included for the following:    (1) fuel cell sealing material, which consists of the rubber composition;    (2) fuel cell, which has the fuel cell sealing material;    (3) hard disk drive top cover gasket, which consists of the rubber composition;    (4) hard-disk drive, which has the hard-disk drive top cover gasket;    (5) wire-connector sealing material, which consists of the rubber composition; and    (6) wire connector, which has the sealing material.    DESCRIPTION OF DRAWING(S) - The figure shows the perspective view of a separator integrated cell seal component for fuel cell.    Separator (1)    Space (2)    Sealing component (3)