A novel triblock copolymer poly(ε-caprolactone)-b-polybutadiene-b-poly(ε-caprolactone) (HTBCP) initiated by hydroxyl-terminated polybutadiene (HTPB) and catalyzed by stannous octanoate ［Sn(Oct)₂］ was synthesized via the ring-opening polymerization of ε-caprolactone（ε-CL）. The copolymers with different molecular weight were prepared by changing the feed ratio of HTPB to ε-CL. The block copolymers were characterized by GPC,FTIR,¹HNMR,TG and DSC. The results show that the molecular weight of copolymers can be controlled by adjusting the feed ratio of ［HTPB］ to ［ε-CL］. TG and DSC indicate that all of the block copolymers exhibit good thermal stability. Their weight loss is less than 5% at 270 ℃ under nitrogen atmosphere. With amount of PCL units increasing,thermal stability of copolymers increases. The copolymers have only one glass transition and melting temperature, which reflect that two kinds of monomers are compatible in copolymer.