Abstract: The mesoporous molecular sieves MCM-41 and Co-MCM-41 containing different cobalt contents were prepared by hydrothermal synthesis method with cobalt nitrate as cobalt source and characterized using X-ray diffraction (XRD), Fourier transform infrared spectrum (FT-IR) and nitrogen adsorption. The characterization results indicate that the well-ordered mesostructure was obtained even when the Co/Si mol ratio was 0.1 and Co has been introduced into the framework of MCM-41. Adsorption removal of basic nitrogen compounds from 0^# diesel oil was studied by static stirring method using MCM-41 and Co-MCM-41. One gram of Co-MCM-41(2) could adsorb 5.324 mg nitrogen from diesel oil while MCM-41 could adsorb 2.532 mg, indicating that the adsorptive denitrification of Co-MCM-41(2) has been enhanced pronouncedly. But the adsorptive denitrification capacity of Co-MCM-41(2) decreased when the Co/Si exceeded 0.06, which could be ascribed to the addition of exceeded Co into the frameworks of MCM-41. The Co was well dispersed in the channel of Co-MCM-41 as Co₃O₄ and blocked the adsorption active sites which hindered the adsorption between the nitrogen compounds and active sites and depressed the adsorptive denitrification capacity. The results of adsorptive denitrification from diesel oil using dynamic adsorption method showed that for a breakthrough point of 10 μg/g, the breakthrough volume and breakthrough capacity of Co-MCM-41(2) at ambient conditions are 35 mL/g-adsorbent and 4.2 mg-nitrogen/g adsorbent, respectively. For MCM-41, both of the two data were almost zero, indicating that MCM-41 almost lost all the adsorptive denitrification capacity due to the shorter contact time and implying that Co-MCM-41(2) had better selectivity on basic nitrogen compounds in 0^# diesel oil.