Aqueous solutions of a blend consisting of a PEO-PPO-PEO triblock copolymer and a PPO-PEO-PPO triblock copolymer were prepared. Thermoreversible micellization and gelation properties of the blend were studied as a function of temperature and molar ratio of two copolymers by means of micro-DSC and rheology. The completely thermoreversible behaviors of micellization and gelation were observed for all solutions with various molar ratios. At a given concentration of the PEO-PPO-PEO copolymer, three effects of the PPO-PEO-PPO copolymer were found: (a) micellization shifted to a lower temperature with increasing the concentration of the PPO-PEO-PPO copolymer, implying a “salt-out” like effect; (b) there appeared a secondary peak due to the interaction between two copolymers, which increased in height with increasing the PPO-PEO-PPO copolymer; and (c) also the significant changes in enthalpy and entropy were shown. The rheological studies allowed the determination of the sol-gel transition, the gel strength, and the polymer-polymer interaction-induced unique features of rheology. The possible mechanism for the PPO-PEO-PPO copolymer induced micellization and gelation will be proposed and discussed.