OEGylation is an attractive approach to modifying poly(amino acid)s. OEG conjugation improves water-solubility of poly(amino acid)s, and confers possible thermal-responsive functionality for the conjugated poly(amino acid)s. Nevertheless, the impact of OEG architecture and the manner in which the OEG moiety interferes with the performances of poly(amino acid)s remain a work in progress. In this study, a series of new linear and Y-shaped OEG-substituted poly(glutamic acid)s were designed and synthesized. It is found that the thermoresponsive behavior of OEGylated poly(glutamic acid)s experiences steric repulsion effect, the strengths of which are architecture and length-dependent, and grows pronounced only when the number of the OEG units is >= 6. Notably, the Y-shaped architecture is able to stabilize the helicity of poly(glutamic acid) backbones, while maintaining higher alpha-helical conformation than its linear counterparts. In sum, our result indicate that Y-shaped architecture is more appropriate toward OEGylating poly(amino acid)s for biomedical applications.