The objective of this study is to get a fundamental understanding of role of surface oxygen-contained functional groups (OCFG) in adsorptive denitrogenation (ADN) of liquid hydrocarbons over activated carbon, and thus to improve the ADN performance of activated carbon through modification of surface chemistry of activated carbon. A set of activated carbon samples with different amount and distribution of OCFG was prepared by oxidative modification and thermal treatment of a commercial activated carbon. The prepared activated carbons were characterized by the temperature-programmed desorption coupled with mass spectrometry for the concentration of various OCFG, and evaluated in a fixed-bed adsorption system using a model fuel containing aniline, indole, quinoline, carbazole, and ethyl-carbazole. The results indicate that OCFG, especially the strong carboxyls, weak carboxyls and anhydrides, play a crucial role in determining the adsorptive performance of activated carbon for selective removal of nitrogen compounds from liquid hydrocarbons. The adsorption mechanism of the nitrogen compounds over activated carbon was discussed on the basis of the structure-performance correlation and the molecular simulation. (C) 2012 American Institute of Chemical Engineers AIChE J, 59: 1236-1244, 2013