A process for producing a polymer composition, which comprises mixing and reacting: as component, an unsaturated group-containing siloxane compound of the following formula: wherein R 1 is a hydrogen atom or a C 1-20 hydrocarbon group, m is an integer of at least 3, a is an integer of from 0 to 10, and the siloxane structure is a chain or cyclic structure, as component, a siloxane compound having a structure of the following formula wherein hydrogen is directly bonded to silicon, wherein R 2 is a C 1-20 hydrocarbon group, n is an integer of at least 3, and the siloxane structure is a chain or cyclic structure, as component, at least one member selected from the group consisting of organic metal compounds of Group 1, 2, 12, 13 and 14 metals of the periodic table, being selected from the group consisting of n-butyllithium, diethylmagnesium, tri-n-decylaluminum, tetraethyltin, tetrabutyltin, a straight chain or branched chain C 1-20 alkylaluminum or alkylzinc, trimethylaluminum, triethylaluminum, tri-n-propylaluminum, tri-n-butylaluminum, triisobutylaluminum, triisoprenylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum, tri(2-methylpentyl)aluminum, dimethylaluminum chloride, methylaluminum sesquichloride, methylaluminum dichloride, diethylaluminum chloride, ethylaluminum sesquichloride, ethylaluminum dichloride, di-n-propylaluminum chloride, di-n-butylaluminum chloride, diisobutylaluminum chloride, isobutylaluminum dichloride, diethylaluminum iodide, diethylaluminum fluoride, diethylaluminum bromide, diisobutylaluminum hydride, diethylaluminum hydride, diethylaluminum methoxide, diethylaluminum ethoxide, diisobutylaluminum methoxide, diisobutylaluminum ethoxide, diisobutylaluminum isopropoxide, dimethylzinc, methylzinc chloride, methylzinc bromide, methylzinc iodide, methylzinc fluoride, diethylzinc, ethylzinc chloride, ethylzinc bromide, ethylzinc iodide, and ethylzinc fluoride, and as component, a metal catalyst of Group 8, 9 or 10 metal of the periodic table, being at least one member selected from the group consisting of metal catalysts of iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium and platinum. as component, an unsaturated group-containing siloxane compound of the following formula: wherein R 1 is a hydrogen atom or a C 1-20 hydrocarbon group, m is an integer of at least 3, a is an integer of from 0 to 10, and the siloxane structure is a chain or cyclic structure, as component, a siloxane compound having a structure of the following formula wherein hydrogen is directly bonded to silicon, wherein R 2 is a C 1-20 hydrocarbon group, n is an integer of at least 3, and the siloxane structure is a chain or cyclic structure, as component, at least one member selected from the group consisting of organic metal compounds of Group 1, 2, 12, 13 and 14 metals of the periodic table, being selected from the group consisting of n-butyllithium, diethylmagnesium, tri-n-decylaluminum, tetraethyltin, tetrabutyltin, a straight chain or branched chain C 1-20 alkylaluminum or alkylzinc, trimethylaluminum, triethylaluminum, tri-n-propylaluminum, tri-n-butylaluminum, triisobutylaluminum, triisoprenylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum, tri(2-methylpentyl)aluminum, dimethylaluminum chloride, methylaluminum sesquichloride, methylaluminum dichloride, diethylaluminum chloride, ethylaluminum sesquichloride, ethylaluminum dichloride, di-n-propylaluminum chloride, di-n-butylaluminum chloride, diisobutylaluminum chloride, isobutylaluminum dichloride, diethylaluminum iodide, diethylaluminum fluoride, diethylaluminum bromide, diisobutylaluminum hydride, diethylaluminum hydride, diethylaluminum methoxide, diethylaluminum ethoxide, diisobutylaluminum methoxide, diisobutylaluminum ethoxide, diisobutylaluminum isopropoxide, dimethylzinc, methylzinc chloride, methylzinc bromide, methylzinc iodide, methylzinc fluoride, diethylzinc, ethylzinc chloride, ethylzinc bromide, ethylzinc iodide, and ethylzinc fluoride, and as component, a metal catalyst of Group 8, 9 or 10 metal of the periodic table, being at least one member selected from the group consisting of metal catalysts of iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium and platinum.