Abstract: Proposed is a moisture-curable polyurethane resin composition having good storage stability under a moisture-free condition without affecting the curability in the presence of moisture. The composition comprises (a) a polyurethane prepolymer as a reaction product of a polyol compound and a polyisocyanate compound, (b) a catalytic compound to promote curing of the composition and (c) a stabilizer which is trifluoromethane sulfonic acid in a limited amount. The improvement in the storage stability of the composition is particularly remarkable when trifluoromethane sulfonic acid is used in combination with a specific curing catalyst. The composition is useful in the preparation of a surgical casting tape by coating or impregnating a flexible substrate web such as a glass fiber cloth therewith.