In the study, we investigated the influence of degree of branching (DB) of isocyanate-functionalized hyperbranched polyurethanes (HPU-NCOX) on the cure and thermal property of phenol-terminated benzoxazine oligomer (BZ(-OH)). The structure of the as-synthesized HPU-NCOX was confirmed by proton nuclear magnetic resonance (H-1 NMR and C-13 NMR), gel permeation chromatography (GPC) and Fourier transform infrared spectra (FT-IR). Thermally activated cross-linking behavior as well as the thermal stability of HPU-NCOX/BZ(-OH) blend was investigated by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). HPU-NCOX can covalently incorporate into BZ(-OH) via urethane reaction. Both the cure kinetics and the weight residue of HPU-NCOX/BZ(-OH) copolymer reveal a gradual increase with the improvement of DB of HPU-NCOX. A novel isocyanate-functionalized hyperbranched polyurethanes (HPU-NCOX) with degree of branching (DB) ranging from 25.1 to 51.1 % were successfully synthesized. The HPU-NCOX and benzoxazine copolymers exhibit enhanced cure kinetics with the increase of DB of HPU-NCOX.