The synthesis of a new class of double hydrophilic block copolymers, namely poly(p-hydroxystyrene-b-methacrylic acid) (PHOS-PMAA), by a combination of anionic polymerization high-vacuum techniques and postpolymerization acidic hydrolysis, is described. A series of PHOS-PMAA copolymers with different molecular weights and compositions have been synthesized, indicating the good control over the molecular characteristics of the final copolymers. The solution behavior of PHOS-PMAA is studied as a function of the solution pH. A number of characterization techniques, including potentiometric titrations, fluorescence and IR spectroscopy, dynamic and electrophoretic light scattering, and atomic force microscopy, are used in an effort to elucidate the structural changes of the block copolymers at different levels, under different pH environments. Experimental results prove the pH responsive self-assembling ability of PHOS-PMAA copolymers.