The synthesis and characterization of new thermoresponsive pegylated poly-L-glutamate (poly-L-EG(x)Glu) are described. The obtained polypeptides display low critical solution temperature (LCST) behaviors in water, and the LCST can be tuned via copolymerization of different amino acid monomers at varied molar ratio. This is the first example of thermoresponsive polypeptide made from ring-opening polymerization of alpha-amino acid N-carboxyanhydrides (NCAs). Circular dichroism characterizations reveal that the secondary structure of poly-L-EG(x)Glu depended on the chain length of the side chain.