Surface-grafted poly(L-glutamic acid) (PLGA) films on silicon oxide surfaces were prepared and examined for their responsiveness to the external stimuli of pH, surfactant (decylammonium chloride), and divalent metal ion (Ca2+) in aqueous solutions. A surface-initiated vapor deposition-polymerization of N-carboxyanhydride of gamma-benzyl L-glutamate was first performed to synthesize surface-grafted poly-(gamma-benzyl L-glutamate) (PBLG) thin films, followed by debenzylating with hydrogen bromide in anhydrous benzene. The successful conversion of surface-grafted PBLG to PLGA films was confirmed by Fourier transform infrared spectroscopy and ellipsometry. The conformational transitions and the corresponding changes in film thicknesses and refractive indices were in situ examined by circular dichroism (CD) and ellipsometry, respectively. The CD study shows that the conformation undergoes a transition between a-helix and random coil at pH 5.75-7. Upon the conformational transition, the film thicknesses and refractive indices change correspondingly. From pH 4 to 8, the helical chains with the average thickness of 170 nm and refractive index of 1.381 change to the random coils of 260 nm and 1.355. Compared to the solvated free PLGA chains, the grafted chains are in favor of helical conformation. The observations of the transitional behaviors induced by decylammonium chloride and Ca2+ lead to similar conclusions.