a-MoO3 nanoplates have been prepared through thermal decomposition of two novel organometallic molybdenum complexes, as new solid precursors, at 500 C for 2 h. The two molybdenum complexes ([(Mo2(bipy)(CO)n(DQ)m]; where, DQ = quinoxaline-2,3-dione; n = 2 or 4, m = 2 or 3) were synthesized by reaction of Mo(CO)6, and DQ in presence of 2,20-bipyridine in THF solvent at reflux temperature under atmospheric or reduced pressure. Interestingly, the crystallite size of the produced MoO3 nanoplates products (80.7 and 114 nm) depended on the organic moiety content of the ignited solid precursor. The as-prepared products were characterized by means of elemental analysis, Fourier transform infrared spectroscopy (FT-IR), UV–Vis spectroscopy, thermal analysis (TGA), X-ray powder diffraction (XRD), Field emission electron microscopy (FESEM) and mass spectroscopy. The produced MoO3 nanoplates showed semiconducting properties by exhibiting optical band gab energy of 3.0 or 3.25 eV.