Abstract: A rubber composition obtained by compounding (B) from 0.005 to 50 parts by weight of an polyorganohydrogensiloxane and (C) from 0.00001 to 1 part by weight of a compound of a transition metal belonging to the group VIII with (A) 100 parts by weight of a rubber-forming polymer mainly comprising (I) from 3 to 70% by weight of a polyorganosiloxane represented by the formula: ##EQU1## wherein R represents a substituted or unsubstituted monovalent organic group, 0.02 to 10 mole % of which being a vinyl group; and a represents a number of from 1.900 to 2.004,and having a degree of polymerization of from 500 to 10,000 and (II) from 30 to 97% by weight of organic rubber, and subjecting the resulting compound to hydrosilylation while effecting shear deformation. The rubber composition is excellent in roll processing properties, mechanical strength, heat resistance, and low-temperature property and is suitable as oil seal and rubber hose.

Abstract: A rubber composition that is prepared by reacting an organic peroxide, under shear deformation, with 3-70 parts by weight of silicone rubber (I), 30-97 parts by weight of a saturated elastomer (II) that substantially fails to be crosslinked with an organic peroxide when it is used alone, and 0-20 parts by weight of another elastomer (III) that is co-crosslinkable with component (I) in the presence of an organic peroxide and which is also co-crosslinkable or highly miscible with component (II) [where (I)+(II)+(III)=100 parts by weight].