Temperaturedependent association behavior of poly(ethylene oxide)poly (propylene oxide)poly (ethylene oxide) (PEOPPOPEO) block copolymers in Bovine Serum Albumin (BSA) aqueous solution has been investigated using pyrene fluorescence spectrum. The critical micellization temperature (CMT) of Pluronics in aqueous solution is increased by the addition of BSA. It is explained by the hydrophobic interaction between BSA and PO block.