An isocyanate-terminated urethane prepolymer which has a low melt viscosity; a process for producing the prepolymer; and an adhesive which comprises the urethane prepolymer and has such satisfactory workability that the adhesive in a molten state can be easily applied to substrates. The process for producing an isocyanate-terminated urethane prepolymer comprises reacting polyols with a polyisocyanate compound, and is characterized in that the polyols comprise 10-60 mass% polyester polyol and 90-40 mass% polycarbonate polyol, 50-100 mass% of the polyester polyol being accounted for by a sebacic acid-derived polyester polyol which is a polycondensate of sebacic acid with a diol compound, and that the polyisocyanate compound and the polyols are reacted in such amounts that the isocyanate group/hydroxy group ratio is 1.2-3.2 (by mol). The adhesive comprises the isocyanate-terminated urethane prepolymer as the main component.