Well-defined amphiphilic poly(epsilon-caprolactone)-b-poly(N-vinylpyrrolidone) (PCL-b-PNVP) block copolymers were successfully prepared via the combination of ring-opening polymerization (ROP) and xanthate-mediated reversible addition fragmentation chain transfer (RAFT) polymerization. Well-defined poly(epsilon-caprolactone) (PCL-OH) was synthesized by ROP in bulk at 110 degrees C using benzyl alcohol as initiator and stannous octate [Sn(Oct)(2)] as catalyst. The OH end group was then converted into its corresponding xanthate (PCL--X) via the conversion to its corresponding bromide (PCL-Br). These are verified by H-1 NMR spectroscopy. PCL-b-PNVP block copolymers were synthesized via RAFT polymerization in tetrahydrofuran (THF) at 80 degrees C using PCL-X as macro-chain transfer agent and characterized by H-1 NMR spectroscopy and gel permeation chromatography (GPC). The amphiphilic diblock copolymer PCL63-b-PNVP90 forms spherical micelles of similar to 34 nm diameter in water as shown by transmission electron microscopy (TEM), supported by H-1 NMR spectroscopy, and light scattering. The critical micellar concentrations were determined by fluorescence spectroscopy using pyrene as probe. The critical micelle concentration (cmc) value of the block copolymers increases with the increase in the chain length of PNVP block. The overall hydrodynamic radius (Rh) of the micelles remains almost constant over the concentration range above the cmc value and over the angles of scattering measurement.