Abstract: A 1D-carbon/carbon composite (C/C) with an organic- modified nanoclay filler was fabricated by hot-pressing and densification at temperatures of 1 000, 1 100, 1 200 and 1 300℃. The organic modified nanoclay was prepared by substituting ions between the layers of an inorganic clay with an organic quaternary ammonium salt. The thermal transformation of the nanoclay following the hot-pressing was investigated by X-ray diffraction and Raman spectroscopy and the effect of the transformation on the bulk density, porosity, thermal conductivity, flexural strength and modulus of the C/C were characterized. The microstructure of the specimens was observed by scanning electron microscopy. Results indicate that the hot-pressing temperature has a significant impact on the structure and properties of the nanoclay-reinforced C/C composite. The C/C composite with the nanoclay filler hot-pressed at 1 200℃ exhibited the best mechanical properties with a flexural strength of 230.1 MPa and modulus of 87.3 GPa. At this temperature, the nanoclay transformed into mullite, cristobalite, disordered nanoclay, ordered carbon and disordered carbon dispersed uniformly in the carbon matrix. This modified the structure of the carbon matrix and tightened the interface between the matrix and the fibers, thus increasing the mechanical properties of the C/C. Carbothermal reduction took place between SiO₂ and the carbon matrix at 1 300℃, which damaged the matrix structure and decreased flexural strength and modulus of the composite. However, the presence of, the reaction product (SiC) increased the thermal conductivity.