The BAB-type triblock copolymers composed of a central poly(ethylene oxide) (PEO, (M) over bar (nPEO) = 1000) block and two poly[(D,L-lactic acid)-co(glycolic acid)] end blocks with molecular weights between 900 and 1600 exhibited an interesting phase transition behaviour. The copolymer aqueous solution can form micelles with PLGA loops in the core and a PEO shell and groups of micelles because of bridging between micelles caused by the PLGA blocks with raising temperature. A possible micellar gelation mechanism was suggested.