A poly(butylene terephthalate)-poly(vinyl chloride) blend made of the solution of the two polymers in N-methyl pyrrolidone has been studied on compatibility between the polymers as well as crystallization mechanism of poly(butylene terephthalate) in the blend. The blend shows a single glass transition temperature which was measured by means of differential scaning calorimeter and dynamic mechanical analyser for tan δ. The g1ass transition temperature of the blend satisfies the Fox equation in all the compositions. The poly(vinyl chloride) content less than 50% in the blend gives little change in the crystallinily of Poly(butylene terephthalate) but the crystallization temperature of poly(butylene terephthalate) decreases with an increase of the poly(vinyl chloride) content in the blend. The poly(vinyl chloride) content more than 50% in the blend causes kinetic hinderance in the crystallization of poly(butylene terephthalate) in the blend.