Epoxy‐amine system is a type of important matrix material for preparation of carbon fiber composites. The amidation of carbon nanotubes (CNTs) has been widely developed for enhancing the mechanical properties of the epoxy resin matrix. However, the various amino‐functionalized CNTs will produce different effect in the same epoxy matrix due to the diversity in reactivity, compatibility, and dispersion stability. In this paper, the amino‐functionalized multiwalled carbon nanotubes (MWCNTs‐NH2) were prepared through surface grafting ethylenediamine and diethyltoluenediamine (DETDA; designated as MWCNTs‐EDA and MWCNTs‐DETDA), and dispersed into epoxy resin matrix in which the DETDA was also used as curing agent. Compared with MWCNTs‐EDA, the MWCNTs‐DETDA showed a better dispersion state and stability in the epoxy resin, and had a relatively small impact on the curing behavior of epoxy matrix. After adding 0.5 wt% MWCNTs‐DETDA, the unidirectional T700 carbon fiber composites exhibited the significantly enhanced interlaminar shear strength and flexural properties due to the uniform dispersion of MWCNTs‐DETDA and the modified interface bonding. The results indicated that the chemical compatibility between MWCNTs‐NH2 and resin matrix can exert an important influence on the microstructure, curing behavior, thermo‐mechanical properties, and mechanical properties of the epoxy resin and the resulting carbon fiber composites. POLYM. COMPOS., 39:E733–E744, 2018. © 2016 Society of Plastics Engineers