This study deals with the interaction between iron oxide nanoparticles and a carbon-rich source (pitch) during the carbonization process, resulting in a carbon material of high added value. The iron oxide nanoparticles were prepared by different procedures in order to obtain Fe2O3 and Fe3O4 with different particle sizes. The results show that the presence of iron oxide modifies the thermal behaviour of the pitch, especially in the temperature range of 400-500 degrees C when the pre-graphitic order in the carbon matrix is formed. The crystalline microstructure of the materials changes from domains to mosaics when iron oxide is added. The oxidation state of the iron is also modified during carbonization due to the presence of the carbon.