TECHNOLOGY FOCUS - POLYMERS - Preferred Composition: The terminal site of reactive silicon group-containing polymer (A) is of formula: O-(-CH2-C(-R2CH(-R3)-CH2-SiR13-aXa)-O)n-R4-CH(-R5)-CH2-SiR13-aXa. The principal chain of reactive silicon group-containing polymer (A) is polyoxyalkylene-type polymer. The reactive silicon group-containing polymer (A) preferably comprises on an average of 1.5 or more reactive silicon groups (I) at one terminal. The curable composition further comprises polymer (B) comprising reactive silicon group (I) other than component (A). The principal chain of reactive silicon group-containing polymer (B) is polyoxyalkylene-type polymer. The reactive silicon group-containing polymer (B) is reactive silicon group-containing polymer (C) comprising on average of 1 or less, or 1.7 or more reactive silicon groups at the one terminal. The reactive silicon group-containing polymer (B) comprises reactive silicon groups at 2 or more terminals, and which is a reactive silicon group-containing polymer (D) comprising on an average of 1 reactive silicon group at the one terminal. The reactive silicon group-containing polymer (D) comprises on an average of 1.5 or more reactive silicon groups. The ratio of reactive silicon group-containing polymer (A) and reactive silicon group-containing polymer (B) in the curable composition is 80/20-5/95.R2,R4=bivalent 1-6C bonding group, where atom bonded with each adjacent C is C, O or N;R3,R5=H or 1-10C hydrocarbyl;andn=0-10 (excluding 0).Preferred Process: The curable composition is obtained by preparing reactive silicon group-containing polymer (A) by reacting 0.6 equivalents or more alkali metal salt on polymer having hydroxyl group at the terminal with respect to a hydroxyl group, reacting the resultant product with epoxy compound having carbon-carbon unsaturated bond, introducing reactive silicon group by hydrosilylation reaction with respect to carbon-carbon unsaturated group, and reacting with halogenated hydrocarbon compound having carbon-carbon unsaturated bond.