Abstract: Phenolic resin was heat-treated up to 2400℃ in an argon flow, leading to the formation of porous graphitized products. The microstructural changes in the graphitized phenolic resin were investigated by transmission electron microscopy. Some oval-shaped crystallites from 20 to 200nm and with very regular order have been found, which extend to the surface of the pores. In general, the larger the pores, the larger are the crystallites inside them, and there are smaller crystallites between the larger crystallites. The formation of the crystallites is due to the gas evolution reaction, evaporation of which creates an effect analogous to stress graphitization, leading to these highly directional crystallites at the edges and inside the pores.