Abstract: A curing composition contains a polymer having two or more thiol groups per molecule, a compound having two or more isocyanate groups per molecule, and carbon black, and further contains a filler of which main ingredient is silicic acid or a silicate, or contains an organic filler of which main ingredient is pulverized coal. The curing composition has satisfactory storage stability of base compound and satisfactory curability event after storage of the base compound and, furthermore, gives a cured compound having sufficient strength at break, hardness, and gas-barrier properties. The curing composition is hence suitable for use as a sealant for insulating glass manufacture, vehicle window frames, etc.