The properties of micelles of Pluronic F68 (F68), a water-soluble triblock copolymer with the average composition (ethylene oxide)78-(propylene oxide)30-(ethylene oxide)78, are studied by fluorescence techniques with octadecyl rhodamine B as a probe. The fluorescence intensity, polarization, and lifetime are observed as a function of F68 concentration or temperature. The results show that the critical micelle concentration (cmc) of F68 is strongly dependent on temperature as suggested by Bahadur et al. from dynamic light scattering (Langmuir 1992, 8, 1903). The cmc’s obtained are 10 g/dL at 20-degrees-C and 0.5 g/dL at 50-degrees-C. From fluorescence anisotropy, the microviscosity of the micelle is estimated to be 1.9 cP at 20-degrees-C and 16 cP at 40-degrees-C. The drastic increase of the microviscosity is attributed to the conformational change of the micelle from a loosely coiled aggregation to a compact structure.