A novel method for measuring the volume porosity of the C/ C-SiC composites based on micro-CT technology was proposed. We first disscussed the principle of this new method, and then investigated the influence of the measurement volume on its accuracy. The results showed that, using micro-CT technology, the 3D microstructures of the C/ C-SiC samples in gray histogram mode were obtained. According to which, the volume porosity of the C/ CSiC samples can be determined through threshold segmentation analysis. And it was of importance to find that a critical measurement volume is needed to obtain the volume porosity with a high accuracy.