An in situ ring-opening polymerization strategy was employed to grow multihydroxyl. dendritic macromolecules on the convex surfaces of multiwalled carbon nanotubes (MWNTs), affording novel one-dimensional (1D) molecular nanocomposites. The crude MWNTs were oxidized using 60% HNO3 and then reacted with thionyl chloride, resulting in MWNTs functionalized with chlorocarbonyl groups (MWNT-COCl). MWNT-COCl, when reacted with an excess of glycol, produced hydroxy-functionalized MWNT supported initiators (MWNT-OH). Using the MWNT-OH as the growth supporter and (BF3Et2O)-Et-. as catalyst, multihydroxy hyperbranched polyethers-treelike macromolecules-were covalently grafted on the sidewalls and ends of MWNTs via in situ ring-opening polymerization of 3-ethyl-3-(hydroxymethyl)oxetane (EHOX). TGA measurements showed that the weight ratio of the as-grown hyperbranched polymers on the MWNT surfaces lay in the 20-87% range. The products were characterized by FTIR, NMR, DSC, TEM, and SEM. TEM indicates that the MWNTs are enveloped evenly by the hyperbranched molecules for samples with greater polymer coatings. The as-prepared nanocomposites exhibit relatively good dispersibility in polar solvents such as methanol, ethanol, DMF, and DMSO. Because of the fact that the hyperbranched macromolecules on the MWNTs contain numerous functional hydroxy groups on their periphery, the functionalized MWNTs can be further functionalized with the merits and advantages associated with dendritic polymers, which would result in a series of fascinating novel nanomaterials and nanodevices.