A model, based on the oxidation kinetics model of unidirectional C/SiC composite (between 400 °C and 800 °C in air, P = 100 KPa), is developed to predict the coefficient of thermal expansion (CTE) of 2.5D C/SiC composites. It takes into account (i) the changes versus time and temperature of the geometry of the notch resulting from the consumption by oxidation of the carbon interphase and fiber, (ii) the accumulation of oxidation damage of the carbon interphase and fiber in C/SiC microcomposite (one single filament) versus temperature during heating, (iii) the multiscale analysis of CTE of 2.5D C/SiC composites. The CTE of 2.5D C/SiC composites in warp direction during heating in air oxidizing environment are evaluated and validated in comparison to experimental data. The results indicate that the predicted CTE of 2.5D C/SiC composites in warp direction agree well with the experimental data.