Thermal expansion of differently-textured pyrolytic carbon matrices (pyrocarbons) of carbon/carbon composites was studied with a high temperature X-ray diffraction at temperatures ranging from 25°C to 1400°C. The composites were synthesized by chemical vapor infiltration of a carbon fiber felt, using methane as a carbon source. From the linear dependence of the lattice displacement on temperature, coefficients of thermal expansion (CTE) of the pyrocarbons were calculated. One-dimensional thermal expansion along the (002)-direction (c-axis) of the pyrocarbons was found to be proportional to the composite synthesis temperature. A correlation between CTE and pyrocarbon texture was found: low-textured pyrocarbon with an extinction angle (Ae) of 10° exhibits a smaller CTE of 2.02 × 10-5 K-1, whereas high-textured pyrocarbon with an Ae of 22° exhibits a considerably higher CTE of 2.65 × 10-5 K-1. However, CTE of high-textured pyrocarbon is still smaller than that of graphite, which is 2.9 ×10-5 K-1.