Abstract: Polyimide modified C/C (C/C-PI) composites were fabricated by needling technology, chemical vapor infiltration (CVI), vacuum impregnation and curing process. The flexural properties, heat conducting properties and thermal expansion properties of C/C-PI composites were investigated. The results indicate that C/C-PI composites show a better flexural strength of 120.75 MPa in XY direction and 40.33 MPa in Z direction which are 17.92% and 20.57% higher than C/C composite. The thermal conductivities of C/C-PI composites do not change significantly with temperature, and reach the maximum values of 29.88 W(m·℃)^-1 in XY direction and 9.93 W(m·℃)^-1 in Z direction, which are 47.02% and 56.12% lower than C/C composites, respectively. As the test temperature continues to rise, the thermal conductivities of C/C-PI and C/C composites are decreasing gradually. The coefficients of linear expansion of C/C-PI composites increase linearly with the increase of temperature and the values maintain under 4×10^-6 K^-1. In particularly, C/C-PI composites have a lower linear expansion coefficient in XY direction in comparison with Z direction, which can meet the requirement of dimension stability of thermal structure parts.