Advances in carbon nanotube (CNT) based composites over the past decade have demonstrated broad potential of utilizing them as multifunctional sensors because of their unique electrical properties. This article studies the thermoresistive behavior of two-component (CNT-epoxy) nanocomposites and hierarchical (CNT-fiber-epoxy) multiscale composites using in situ electrical resistance measurements during thermal cycling from 25 to 145 °C. A series of CNT-based composites with controlled nanotube morphologies were created via three-roll-milling, dip-coating and electrophoretic deposition methods. The results show that the thermoresistive behavior of CNT-based composites is influenced by the CNT concentration, thermal expansion, fiber/polymer properties, and interfacial interactions. CNT-epoxy nanocomposites with randomly dispersed CNTs show a positive temperature correlation. In comparison, multiscale composites with fibers show a double-crossover-shaped temperature dependence of their electrical resistance influenced by the changes of the CNT network that are induced by the polymer thermal motions and the residual thermal stresses. The thermal expansion behavior of the composites was characterized using a thermomechanical analyzer and a simplified finite element model was used to qualitatively examine the fiber-matrix interfacial residual stresses. While the thermoresistive behavior of nanocomposites has been investigated more broadly, this research is a first step in understanding the processing-structure-thermoresistive response relationship of multiscale CNT/fiber composites.