A curable composition having good curability and adhesion comprising: (A) an reactive silicon group-containing organic polymer, (B) a titanium chelate represented by the general formula (1) or (2) and (C) a high molecular weight plasticizer having a number average molecular weight of 1,000 to 15,000. General formula (1): ##STR00001## wherein each of n R.sup.1s is independently a substituted or unsubstituted hydrocarbon group having 1 to 20 carbon atoms, each of (4-n) R.sup.2s is independently hydrogen atom or a substituted or unsubstituted hydrocarbon group having 1 to 20 carbon atoms, each of (4-n) A.sup.1s and (4-n) A.sup.2s is independently --R.sup.3 or --OR.sup.3 where R.sup.3 is a substituted or unsubstituted hydrocarbon group having 1 to 20 carbon atoms, n is 1, 2 or 3. General formula (2): ##STR00002## wherein R.sup.2, A.sup.1 and A.sup.2 are the same as defined above, R.sup.4 is a substituted or unsubstituted divalent hydrocarbon group having 1 to 20 carbon atoms.