The polymerization of epsilon-caprolactone (CL) in the presence of HCl center dot Et2O via activated monomer mechanism was performed to synthesize diblock copolymers composed of methoxy polyethyleneglycol (MPEG) and poly(epsilon-caprolactone) (PCL). The obtained PCLs had molecular weights close to the theoretical values calculated from the CL to MPEG molar ratios and exibited monomodal GPC curves. We successfully prepared MPEG and PCL diblock copolymers by activated monomer mechanism. The micellar characterization of MPEG-PCL diblock copolymers in an aqueous phase was carried out by using NMR, dynamic light scattering, AFM and fluorescence techniques. The diblock copolymers formed micelles with a critical micelle concentration (CMC) ranging 2.07 x 10(-2) - 1.16 x 10(-3) mg/mL depended on the block lengths of diblock copolymers. The diameters of micelles, measured by dynamic light scattering, were 100-250 nm. Most micelles exhibited a spherical shape in AFM.