Oil-dispersed WS2 catalysts were prepared in situ using an oil-soluble W precursor of W(CO)(6) in the hydro cracking (HCK) of vacuum residue (VR). Smaller size of WS2 catalyst (WS2-DMDS) was also obtained by the addition of dimethyl disulfide (DMDS) with the W precursor in the VR HCK. The activity tests were performed in a batch reactor at 692 K at 9.5 MPa H-2 with the same metal loading of 0.113 mmol. Oil-dispersed MoS2 catalyst was also employed to compare the structure and activity with WS2. Extended X-ray absorption fine structure (EXAFS) and transmission electron microscopy (TEM) analysis were used to examine structural properties of the dispersed catalysts. The activity based upon the H-2 consumption rate per lateral metal numbers, TOFs, in the VR HCK turned out that WS2 (0.709 s(-1)) is better than MoS2 (0.573 s(-1)), which leads to higher asphaltene conversion for WS2 (39.2%) than MoS2 (35.8%). Moreover, it was noted that the dispersibility of WS2 (58.0%) was found better than MoS2 (3.3%).