Four unidirectional pitch-based C/C composites were densified by multiple melted pitch impregnation under vacuum followed by recarbonization to 1273 K. The pitches used for the impregnation were the same pitches used as carbon matrix precursors in the preparation of the C/C composites. Recarbonization steps in one of the composites were also performed under pressure in order to study the effect of pressure during the densification process. The efficiency of the impregnation was evaluated in terms of the voids accessible to the impregnant and was followed by the weight gain during the process and polarized-light microscopy of impregnated composites. Wide differences in the densification process were observed dependent primarily on the physical and chemical properties of the pitch, especially the carbon yield and pitch fluidity. The composites at different stages of densification were characterized by standard procedures (bulk density and porosity), and microscopical techniques (polarized-light microscopy, image analysis and scanning electron microscopy). On the basis of results a mechanism describing the whole process involved in the densification of unidirectional C/C composites is proposed.