PURPOSE: To obtain a composition which has excellent storage stability and cures at a low temp. to give a cured composition free from discoloration by using a specific complex catalyst as a reactive curing catalyst for an epoxidized compound.

CONSTITUTION: An epoxidized compound (A) is mixed with a compound (B) having reactive silicon groups and a tin chelate catalyst (C). The epoxy groups in the ingredient (A) especially preferably are alicyclic ones. Examples of the ingredient (A) include a polymer obtained by polymerizing an epoxidized ethylenic monomer optionally with another kind of ethylenic monomer. The reactive silicon groups of the compound (B) each comprises a hydrolyzable group, preferably an alkoxyl, directly bonded to a silicon atom. Examples of the ingredient (B) include a (co)polymer of an ethylenic monomer containing a reactive silicon group. The ingredient (C) is desirably an oxygen compound, preferably capable of forming a keto-enol tautomer. Examples thereof include acetoacetic esters and β-diketones.