Thermoreversible sol-gel transition of the PEO-PPO-PEO triblock copolymer(Pluronic F127) aqueous solution was monitored by dielectric behavior measurement. Thermoreversible gelation originates from the micelle formation and micelle volume change due to PEO-water, PPO-water LCST behavior. Micelle volume fraction is the critical parameter that dominates the sol-gel transition behavior of Pluronic aqueous solution. By measuring the dielectric constant of 5-22% Pluronic F127 aqueous solution, critical micelle temperature and micelle volume fraction was obtained. The micelle volume fraction of the gel region exceeded the critical volume fractions of simple cubic packing(0.523). Gelation temperature determined by dielectric measurement agreed well with that determined by the tube tilting method.