Carbides and nitrides have attracted considerable interest as catalysts for a variety of reactions including those involving feedstocks containing sulfur. Molybdenum carbide and nitride catalysts are known to have higher hydrodesulfurization (HDS) activities than conventional sulfide catalysts. Carbides and nitrides have also been reported to be resistant to sulfur poisoning, however, the basis for their sulfur tolerance is not well understood. In this work, we studied the interaction of various organosulfur compounds with several early transition metal carbides and nitrides. The materials were prepared from their corresponding oxide precursors using temperature program reaction methods. The carburization or nitridation was carried out using either a mixture containing 15% CH4 in H 2 or NH3, respectively. The interactions of molybdenum carbides and nitrides with organosulfur compounds including thiophene, benzohiophene (BT), dibenzothiophene (DBT), and tetrahydrothiophene (THT) were investigated. X-ray diffraction (XRD) indicated that bulk sulfides were not formed on exposing these materials to sulfur compounds indicating that the interaction with sulfur was limited to the surface. These interactions depended on the types of solvent used and pretreatment conditions employed. Characteristics of the adsorption sites were elucidated using CO2, NH3, and H2 as base, acid, and metal probes, respectively. Equilibrium adsorption isotherms for the adsorption of thiophene, BT, DBT, and THT were Langmuirian, suggesting that the heat of adsorption did not vary significantly with coverage. The mechanisms for sulfur adsorption on Mo2C and Mo2 N were dictated by the availability of acid, base, and metallic sites. From the equilibrium adsorption isotherms and temperature programmed desorption (TPD) experiments, the acid sites on Mo2C and Mo2N played a role in thiophene and BT adsorption. Tetrahydrothiophene adsorption capacity showed insignificant change over Mo2C and Mo2N as different sites were blocked prior to sulfur adsorption. However, the mechanisms of adsorption on these surfaces were different.