PURPOSE: To titled composition, consisting of a liquid rubber-like polymer having carboxyl groups, liquid rubber-like polymer having no functional group and a tetraalkyl titanate, and having suitable sealing property without giving a bad influence on the physical properties of the rubber-like polymers, e.g. in a tire.

CONSTITUTION: A sealant composition obtained by mixing a composition containing (A) a liquid rubber-like polymer having 2W15 carboxyl groups as functional groups in one molecule, e.g. liquid isoprene rubber or liquid butadiene rubber and (B) a liquid rubber-like polymer having no functional group with 1W20wt%, based on the weight of the component (A), tetraalkyl titanate, preferably having 3W8C alkyl groups, e.g. tetra-n-butyl titanate as a crosslinking agent. The resultant composition is capable of easily forming a puncture preventing layer on the inner surface of a tire, maintaining the suitable tackiness and strength, and producing little change with time for a long term without causing the deviation in running.