Well-defined amphiphilic poly(N-vinylpyrrolidone)-b-poly(epsilon-caprolactone) (PVP-b-PCL) block copolymers were synthesized at 30 degrees C using a hydroxyl-functionalized xanthate reversible addition-fragmentation chain transfer (RAFT) agent, 2-hydroxyethyl 2-(ethoxycarbonothioylthio)propanoate, as a dual initiator for RAFT polymerization and ring-opening polymerization (ROP) in a one-pot procedure. Hydrophilic PCL blocks were first synthesized via the ROP of epsilon-caprolactone (CL) using diphenyl phosphate as a catalyst followed by the RAFT polymerization of N-vinylpyrrolidone (VP) by the addition of VP and 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) (V-70) to the reaction mixture. VP quenched the ROP of CL, and V-70 initiated the RAFT polymerization of VP. The resulting PVP-b-PCL block copolymers showed very narrow molecular weight distributions, indicating that the ROP and RAFT polymerization proceeded independently in a controlled manner. To the best of our knowledge, this one-pot process is the most convenient method for the synthesis of PVP-b-PCL block copolymers. The PVP-b-PCL block copolymers could be labeled fluorescently through a reaction with rhodamine B isothiocyanate in the same pot.