We studied the role of multiwalled carbon nanotubes (MWCNTs) on microphase separation and hard domain assembly in the thermoplastic polyurethane/multiwalled carbon nanotube nanocomposites via combination of rheology and thermal analysis (DSC and DMA). The strong solid-like response observed at low frequency together with very low rheological percolation threshold (0.15 wt%) shown by the samples at their disordered state temperature revealed great capability of TPU in dispersing MWCNTs. The results of microphase separation kinetics measured for the fast-cooled samples using the time sweep experiments under isothermal condition together with thermal analysis showed a significant enhancing effect of MWCNTs on accelerating kinetics as well as promoting the extent of hard domain formation. These results could be attributed to increased thermodynamic incompatibility between hard and soft domain of TPU matrix as a result of greater affinity of MWCNTs with hard segments. This allowed the MWCNTs to act as attractive platforms for formation and assembly of hard domains. POLYM. ENG. SCI., 55:2163-2173, 2015. (c) 2015 Society of Plastics Engineers