The interfacial shear strength and fracture behavior of carbon nanotubes (CNT)-grafted polyacrylonitrile (PAN)-based single carbon fiber/epoxy was investigated. Interfacial shear tests of the CNT-grafted and as-received single carbon fiber/epoxy were performed on a microdroplet test fixture using a universal testing machine. It was found that the grafting of CNT improves the interfacial shear strength of single carbon fiber/epoxy. The fractured surface of the microdroplet composite in the CNT-grafted fiber showed rough surfaces with original surface feature and some adhesion of resins. However, the microdroplet composite in the as-received fiber had smooth surface with original fiber surface feature.