The carbonization behavior of petroleum pitch have been investigated b
y in situ high-temperature C-13-NMR at 390-degrees-C, The changes in t
he chemical structure, molecular mobility, and mesophase formation pro
cess of the pitch have been quantitatively monitored simultaneously us
ing in situ high-temperature C-13-NMR. The initial stage of mesophase
formation could be monitored at around the content level of 2%. The ch
anges of aliphatic structure were clearly observed using NMR spectra o
f long-side-chain carbons and alpha-methyl carbons. The early stage of
carbonization was divided into several steps and characterized. The c
hanges in molecular mobility and in chemical structure were closely re
lated to the mesophase transformation.