It seems that the hardening reaction of acetone-furfural resin (A-F resin) is a condensation polymerization eliminating water, receiving more or less oxidation. The carbonization reaction of A-F resin is mainly dehydration up to HTT about 250®C In the range between HTT about 250®C and HTT about 500®C dehydration is combined with decarbonylation and decarboxylation. Dehydrogenation predominates above HTT about 500®C with demethanation.The variation of specific density against HTT shows that Vitro Carbon (A-F resin carbon) is a typical non-graphitizing carbon. The aromaticity and the ring condensation of Vitro Carbon below HTT 1000®C were deduced by the graphical densimetric method of van Krevelen. The aromaticity increases with HTT and reaches a maximum value of unity at HTT about 600®C. The ring condensation index increases above HTT about 500®C and reaches 0.85 at HTT 1000®C.