Abstract: Poly(ε-caprolactone)-block-polystyrene (PCL-b-PSt) was prepared by nitroxide-mediated radical polymerization of styrene (St) in the presence of PCL with terminated-nitroxide radical group (PCL-T) together with the ring-opening polymerization of ε-CL with 4-hydroxyl-2, 2, 6, 6-tetramethylpiperidinyl-1-oxy (HTEMPO) as initiator. 1H-NMR, ESR, FT-IR, GPC and TGA were employed to analyze the structure and properties of the polymers. Results show that the presence of the nitroxide radical has no effect on the ring-opening polymerization of ε-CL. Also, the ring-opening polymerization of ε-CL with Sn(Oct)2 as the catalyst does not destroy the nitroxide radical group. The well-defined PCL-b-PSt copolymers were synthesized through the polymerization of St at the mediation of PCL-T and the mechanism of polymerization of St fulfilled a typical well-controlled polymerization. The thermal stability of PCL-b-PSt copolymer is better than that of PCL homopolymer.