By using a thermally induced phase separation (TIPS) technique, a poly(gamma-glutamic acid) (PGA) monolith was prepared from a polymer solution in which submillimeter-sized salt particles were dispersed. The monolith was then subjected to internal crosslinking reaction with hexamethylene diisocyanate (HDI), followed by washing off the salt particles with water. This simple procedure was found to successfully furnish a unique solid material in which submillimeter-sized cavities are uniformly distributed over a monolithic 3-D microporous network created by the phase separation. This characteristic structure was indeed confirmed by cross-sectional analysis using scanning electron microscopy (SEM). A large surface area (53 m(2)/g) was suggested by the Brunauer Emmett Teller (BET) method. Moreover, remarkable pH-responsivity was demonstrated in terms of fully reversible expansion-shrinkage and capture-release of copper(II) ion. On this basis, the present monolith has promising prospects for a wide range of applications, especially in biomedicine, biotechnology and environmental arena. (C) 2013 Elsevier Ltd. All rights reserved.