To provide a new two-pack type sealing material composition capable of improving a dynamic following property which is the fault of a polysulfide sealing material, capable of solving the problems of weather resistance, heat resistance, foaming properties and the like which are the fault of a polyurethane sealing material, and suitable for the use in outer matter, especially a joint between metal plates.

This sealing material composition is characterized in that the composition contains (a) a polysulfide-polyether polymer and (b) a polyether polyol in the ratio of the components (a)/(b) regulated so as to be (10/90)-(50/50) as base material components, and (c) a compound having two or more isocyanate groups in the molecule and/or a urethane prepolymer modified thereby, regulated so that the ratio of the isocyanate group in the component (c) to the active hydrogen-containing group in the components (a) and (b) may be 0.5-2.0 [ratio of equivalents]. Preferably, a part or the whole of the polyether polyol (b) is (d) an ethylene oxide adduct, and the content of the ethylene oxide component (d) based on the amount of the polyether polyol is 1-50 wt.%.