Abstract: The effects of heat treatments on the crystallization behavior of polyamide 6 (PA6) on the surface of carbon fiber (CF) and their interfacial properties were explored. The effects of heat treatments on the crystallization behavior of PA6 on the surface of CF were characterized by differential scanning calorimetry (DSC) and polarizing microscope (POM) observation. The results show that the PA6 segments are rearranged during the heat treatment to form small and imperfect new crystals, which leads to the increase of crystallinity and the improvement of interfacial transcrystallization morphology. The interfacial property of CF/PA6 composites was characterized by micro-debonding test and unidirectional CF/PA6 composites transverse tensile test. It is revealed that the decrease of the weak interface and the stress concentration lead to the increase of the interfacial shear strength and the decrease of the fracture energy per unit volume of the annealed samples of CF/PA6 composites.