A facile strategy for the free radical polymerization and coupling of -OH groups and -NCO groups in one pot was carried out to synthesize hyperbranched poly(6-O-methacryloyl mannose/2-isocyanatoethyl methacrylate)s [HGP(MaM-co-IM)s]. The effects of the reaction conditions on the molecular parameters of HGP(MaM-co-IM)s were investigated in detail. The key molecular parameter, degree of branching (DB), was estimated from the content of elemental nitrogen that existed solely in the branching units. The DB values and molecular weights of HGP(MaM-co-IM)s can be tuned by the feed ratio of MaM/IM and the reaction time, respectively. Moreover, a mechanism for this one-pot method was proposed with the assistance of H-1 nuclear magnetic resonance (NMR), C-13 NMR, multidetector size exclusion chromatography, elemental analysis, and Fourier transform infrared spectroscopy. In addition, the performance parameters of HGP(MaM-co-IM)s, including loading capacity, biodegradability, and ability to inhibit hen egg white lysozyme fibrillation, were also studied, and the results suggested that HGP(MaM-co-IM)s will have broad applications in the biochemical field.