Biomimetic poly(amidoamine)-poly(benzyl L-glutamate) (PAMAM-PBLG) amphiphiles with multi-armed architecture were synthesized by the ring-opening polymerization (ROP) of β-benzyl-L-glutamate N-carboxyanhydride (BLG-NCA) using primary amine-terminated PAMAM dendrimer as the macroinitiator. Both 1H NMR and 13C NMR demonstrated that all the primary amines of PAMAM participated in initiating the ROP of BLG-NCA monomer, and the chain length of PBLG can be adjusted linearly by the molar ratio of BLG-NCA monomer to PAMAM. These multi-armed PAMAM-PBLG amphiphiles exhibited both α-helix and β-sheet conformations similar to linear analogues, while their multi-armed architecture could enhance the secondary conformation content of PBLG segments. Meanwhile, the PAMAM-PBLG amphiphiles showed weaker liquid crystalline textures than the linear analogues. Moreover, spherical nanoparticles could be generated by direct injection of these PAMAM-PBLG solutions into distilled water, and their average size (38 - 275 nm) could be adjusted through the multi-armed architecture, the PBLG composition, and the concentration of the amphiphiles. These nanoparticles were stable in aqueous solution for up to 64 days at room temperature and 16 days at 37°C. Consequently, this will provide a convenient method not only to synthesize multi-armed polypeptides amphiphiles, but also to generate biodegradable and biocompatible nanoparticles with adjustable size for drug/gene release.