Shape memory composites of hyperbranched polyurethane (HBPU) and acid-treated multi-walled carbon nanotubes (MWNTs) were prepared using an in situ polymerization method. HBPUs with different hard segments contents were synthesized via the A(2) + B-3 approach using poly(ethylene glycol) (PEG) as a soft segment, 4,4'-methylene bis(phenylisocynate), castor oil, and 1,4-butanediol as hard segment. Compared to HBPU, the HBPU/MWNT composites showed faster shape recovery and double the shape recovery stress in the thermomechanical shape memory test, which was dependent on the MWNTs content and HBPU hard segment content. The water-responsive shape memory effect of HBPU/MWNT composites was considered to result from the combined contribution of hydrophilic PEG and well dispersed MWNTs in highly branched HBPU molecules. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 127: 2670-2677, 2013