The effect of block sequence. on the self-assembly of ABC terpolymers; in selective solvent (water/THF) was explored based on two kinds of terpolymers: polystyrene-block-poly(ethylene oxide)-block-poly(acrylic acid) (PS-b-PEO-b-PAA) and PEO-b-PS-b-PAA with the same component, comparable molecular weight, but different block sequence. Copolymer PS-b-PEO-b-PAA has a higher critical water content (CWC) and larger aggregates size than PEO-b-PS-b-PAA. Furthermore, they presented vesicles with hundreds of nanometers at 25% water content which was not observed in the case of PEO-b-PS-b-PAA. It was also found that there was a sharp jump of both the scattering light intensity and average aggregate size for PS-b-PEO-b-PAA. The kinetics of morphological transitions vs the water content was described to explain this phenomenon.