Diblock copolymers composed of poly(gamma-benzyl L-glutamate) and poly(N-isopropylacrylamide) (PNIPAAm) (abbreviated as GN) were prepared by the ring-opening polymerization of gamma-benzyl L-glutamate N-carboxy anhydride (BLG-NCA) using amine-terminated PNIPAAm as a polymeric initiator. Polymeric micelles consisting of PBLG as the hydrophobic inner core and PNIPAAm as the hydrophilic outer shell were prepared by diafiltration method. Their critical micelle concentrations (cmc) were determined by fluorescent probe techniques with pyrene as a hydrophobic probe. The cmc of the polymeric micelle with the thermosensitive outer shell is less influenced by temperature than the ordinary polymeric micelle consisting of PBLG as the same innercore and poly(ethylene oxide) (PEO) as the hydrophilic outer shell (abbreviated as GE). Fluorescence results were used to estimate the thermodynamic data of micelle formation, such as the standard Gibbs energies (Delta G(0)), the standard enthalpies (Delta H-0), and the standard entropies (Delta S-0) of micellization. For the GN/water system, Delta S-0 was found to be positive and so was favorable to micelle formation whereas Delta G(0), Delta H-0, and Delta S-0 for the GE/water system were found to be negative. The partition constant of pyrene in these micelles has a value of the order of 5 and inflection of the change of that for GN with temperature was found around the LCST of PNIPAAm.