Asphaltenes-free vacuum resid derived deasphalted oils (DAOs) from Chinese Liaohe (LDAO) and Venezuela Orinoco (VDAO) were subjected to catalytic hydrotreating. Electrospray ionization (ESI) Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS) analyses were performed on LDAO and VDAO before and after hydrotreating to determine the structural composition transformation of nitrogen-containing compounds as a result of hydrotreating. The results showed that the basic nitrogen contents of the two DAO before and after hydrotreating were relatively constant. However, the neutral nitrogen contents of hydrotreated LDAO and VDAO were dramatically reduced. The LDAO had a higher neutral nitrogen conversion than VDAO, even though LDAO had a higher neutral nitrogen content than VDAO prior to hydrotreating. The significant difference in nitrogen removal for the DAOs was due to the structural variation of the neutral nitrogen compounds. By plotting the double bond equivalent (DBE) value as a function of carbon number for NI class species, the hydrodenitrogenation reactivities of nitrogen compounds could be classified as easy- and hard-to-convert nitrogen compounds. The easy-to-convert nitrogen compounds have more unsaturated cores and have less and/or shorter alkyl side chains than the hard-to-convert nitrogen compounds which have long alkyl side chains.