Hyperbranched poly(urea-urethane)s (HPU) were covalently grafted onto the surfaces of multiwalled carbon nanotubes (MWNT) terminated with multihydroxyl groups by a grafting-from technique using one-pot polycondensation of diethanolamine (DEOA) and tolylene 2,4-diisocyanate (TDI). Core-shell nanostructures with MWNT as the hard core and HPU trees as the soft shell were formed after the latter was attached to the former. The grafted-HPU thickness on MWNT could be well-controlled by adjusting the feed ratio of TDI to DEOA. The solution rheology of the HPU-functionalized MWNTs was investigated for the first time by steady shear measurements. Large numbers of proton-donor and proton-acceptor groups were located in the HPU-functionalized MWNT; intra- and intermolecular H-bonds were easily formed by their interactions. At low temperature, shearing forces induce the conversion from intra- to intermolecular H-bonds. Therefore, these solutions exhibited typical shear-thickening behaviors at low shear rates and behaved as Newtonian fluids at high shear rates. At high temperature, H-bonds in the HPU-functionalized MWNT were destroyed, and the packed structures of HPU trees became more loosed. Thereby, the entanglements between two HPU chains, HPU chains and MWNT, and two neighboring MWNTs were formed, which results in an increase in the connectivity and intensity of associated networks with an enhancement in the initial viscosity. With increasing shear rates, disentanglements and orientation of polymer chains and MWNTs lead to shear-thinning at low shear rates and Newtonian behavior at high shear rates. The rheological behaviors of the HPU-functionalized MWNT solutions showed a strong dependence on concentration, temperature, and thermal and shearing prehistory. A mechanism based on H-bond-driven interactions was proposed to account for the novel rheological behaviors of the HPU-functionalized MWNT solutions.