PURPOSE: To provide a two-component foamable polyurethane sealing material composition comprising a combination of a specified base with a curing agent solution, wherein a specified compound is used as the thixotropant in the base, not staining a transparent base material, and having excellent antisagging properties.

CONSTITUTION: The sealing material composition comprises a combination of a base (A) comprising a polyol having an overall weight-average OH value of 10-250mgKOH, a catalyst (e.g. triethylenediamine), a blowing agent (e.g. water), a foam stabilizer (e.g. perfluoroalkylcarboxylic acid surfactant and a thixotropant with a curing agent solution (B) comprising a polyisocyanate and/or a modified polyisocyanate having at least two terminal NCO groups (e.g. diphenylmethane diisocyanate) in a weight mixing ratio B/A of (0.9-1.1)/1. The thixotropant is a polymercapto compound [e.g. trimethylolpropane tris (thioglycolate)].