New dioxomolybdenum(VI) complexes were obtained by the reaction of [MoO ₂(acac)2] with isonicotinoylhydrazone ligands derived from 2-hydroxy-3-methoxybenzaldehyde (H ₂L ¹) or 2-hydroxy-1-naphthaldehyde (H ₂L2). Isonicotinoylhydrazonato ligands are coordinated to molybdenum as tridentate ONO-donors. Octahedral coordination of each molybdenum atom is completed by methanol (in 1) or by DMSO molecule (in 2). The complexes were characterized by means of chemical analyses, IR spectroscopy and NMR measurements. The molecular structures of the complexes [MoO ₂L ¹(CH3OH)] (1) and [MoO ₂L2(DMSO)] (2) have been determined by single crystal X-ray crystallography.