SiO2- and Al2O3-supported MoS2 and WS2 catalysts were prepared to exploit the evaluation technique of the edge dispersion of MoS2 and WS2 particles. A chemical vapor deposition (CVD) technique using Co(CO)(3)NO as a probe molecule was used for the evaluation. Results were compared with those from conventional techniques such as NO adsorption and TEM. A proportional correlation was obtained between the amount of NO adsorption and the amount of Co atoms accommodated by the CVD technique on WS2/SiO2 and WS2/Al2O3 catalysts, demonstrating a selective location of the Co atoms on the edges of WS2 particles, as previously established for MoS2 catalysts. A comparison of the amounts of NO adsorption and Co accommodation on MoS2 and WS2 catalysts suggested a 70% higher density of sulfur vacancy on MoS2 particles than on WS2 particles regardless of the support. The Co atoms on the edges of MoS2 and WS2 particles showed the identical NO adsorption property. We propose that Co(CO)(3)NO can be used as a probe molecule to evaluate and directly compare the edge dispersions of MoS2 and WS2 catalysts. The dispersion of MoS2 particles was about two times higher than that of WS2 particles with the SiO2-supported catalysts. With the Al2O3-supported catalysts, MoS2 and WS2 particles were dispersed to a similar extent but much more highly dispersed than the counterparts in the SiO2-supported catalysts. The evaluation of the edge dispersion of MoS2 and WS2 Particles by means of TEM may pose problems when SiO2- and Al2O3-supported catalysts are compared. The edges of unpromoted MoS2 particles exhibited a significantly higher intrinsic activity for the HDS of thiophene than those of WS2 particles. (c) 2005 Published by Elsevier B.V.