Mono(dithiolene)sulfidomolybdenum(IV) complexes, [MoS(S-4)(bdt)](2-) (2) and (MoS(S4)(bdtCl(2))](2-) (3) (1,2-benzenedithiolate = bdt, 3,6-dichloro-1,2-benzenedithiolate = bdtCl(2)), were prepared by the substitution reaction of a tetrasulfido ligand in known [MoS(S-4)(2)](2-) (1) with the corresponding dithiol. Complexes 2 and 3 were irreversibly oxidized to give bis(mu-sulfido) dimolybdenum(V) species, {[MoS(bdt)](2)(mu-S)(2)}(2-) (4) and {[MoS(bdtCl(2))](2)(mu-S)(2)}(2-) (5), in aerobic acetonitrile. Mono(dithiolene)oxomolybdenum(IV) complexes, [MoO(S-4)(bdt)](2-) (7) and [MoO(S-4)(bdtCl(2))](2-) (8), that are oxo derivatives of 2 and 3 were also synthesized from a known [MoO(S-4)(2)](2-) (6) of an oxo derivative of 1 and the corresponding dithiol. Further, the electrophilic addition of dimethyl acetylenedicarboxylate to 7 gave [MoO(bdt)(S2C2(COOMe)(2))](2-) (9), and ligand substitution of the tetrasulfido group of 7 with bdt and bdtCl(2) yielded [MoO(bdt)(2)](2-) (10) and [MoO(bdt)(bdtCl(2))](2-) (11), respectively. New sulfido/oxo molybdenum complexes were characterized by H-1 NMR, IR, ESI-MS, Raman, and UV-vis spectroscopies; cyclic voltammetry; and elemental analysis, and crystal structures of 2, 3, 5, 7, and 8 were determined by X-ray analysis.