Abstract: Catalytic cracking diesels （LCOs）from different sources were used to analyze the nitrogen compound distributions in the full fraction and narrow fractions. The hydrodenitrogenation（HDN） reactions of different nitrogen compounds in LCO were investigated. The results showed that indoles and carbazoles are the major components in poor LCO，where anilines account for a small fraction. Additionally，anilines and indoles are mainly in the light fraction，while carbazoles in heavy fractions. The total nitrogen content increases as the boiling point increase，meanwhile a strong increase of carbazoles is observed in over 320 ℃ distillates. The nitrogen distributions of different LCOs have good consistency. The HDN of LCO showed that the reactivity of carbazoles is lower than that of anilines and indoles. The more carbon number in carbazole molecules, the more difficult it is to be removed. In HDN reaction of inferior LCO，a new nitrogen compound, phenylindole, is identified. With the decrease of final boiling point of LCO，the content of carbazoles decreases，HDN activity increases，while no phenylindole is detected.

Key words: LCO, nitrogen compound, hydrodenitrogenation