In　the　study,　isocyanate-functionalized　hyperbranched　polyurethane　(HPUNCO)　with　a　degree　of　branch　of　35.2%　was　synthesized　via　an　A(2)+B-3　method.　This　novel　HPUNCO　was　used　to　fabricate　a　blend　system　with　hydroxyl　groups　bearing　benzoxazine　precursor　(BZ(OH))　to　investigate　its　effective　on　the　thermal　properties　of　BZ(OH).　The　structure　of　HPUNCO　is　confirmed　by　Fourier　transform　infrared　(FTIR)　and　nuclear　magnetic　resonance　spectroscopy.　The　curing　behavior　of　the　reactive　HPUNCO/BZ(OH)　blend　is　investigated　via　differential　scanning　calorimetry　and　FTIR　analyses.　HPUNCO/BZ(OH)　blend　indicates　two　successively　broad　exotherm　peaks　centered　at　132　and　204　degrees　C,　respectively,　which　is　obviously　different　from　that　of　BZ(OH)　with　one　broad　peak　centered　at　206　degrees　C.　Thermogravimetric　analysis　results　confirmed　that　the　thermal　stability　was　enhanced　and　the　char　yield　of　BZ(OH)　was　increased　from　34.3　to　43.2%　by　cocuring　with　10　wt%　HPUNCO.　POLYM.　ENG.　SCI.,　55:604-613,　2015.　(c)　2014　Society　of　Plastics　Engineers