PURPOSE: To obtain titled sealant curable without any crater development, by incorporating a polydiorganosiloxane with each specific amount of an Si-H bond- contg. polyorganohydrogensiloxane, an isocyanate group-contg. organic compound, etc.

CONSTITUTION: The objective sealant can be obtained by incorporating (A) 100pts.wt. of a polydiorganosiloxane with its end hindered by silanol group, having a viscosity of 500W200,000cSt. (at 25°C). with (B) 0.5W15pts.wt. of an organosilicon compound having in one molecule, organoaminoxy group directly bonded to two or more silicon atoms, (C) 0.005W2pts.wt. of a polyorganohydrogensiloxane having, in one molecule, both organic group and hydrogen atom directly bonded to silicon atom, with the amount of said hydrogen atom being 5W 50mol% based on the total of the organic group and the hydrogen atom, also having, in one molecule, two or more hydrogen atoms, (D) 0.005W5pts.wt. of an isocyanate group-contg. organic compound, and (E) 5W300pts.wt. of an inorganic filler.

EFFECT: Capable of affording elastomers with smooth surface.