A mild one-pot hydrothermal route has been successfully designed to controllably prepare orthorhombic alpha-MoO3 nanobelts and monoclinic MoO2 microaxletrees respectively by adjusting the dosage of (NH4)6M07O24 x 4H2O (AHM). The products are characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and UV-visible absorption spectrum. The as-prepared alpha-MoO3 nanobelts, with widths of 100-400 nm and lengths up to 30-40 microm, grow along  direction. The as-obtained MoO2 microaxletrees are assembled by countless nanolaths with the thickness of 80-150 nm. The chemical reaction processes for the formation of MoO(x) (MoO3 and MoO2) phases are investigated based on the experimental phenomena. The possible growth mechanisms are also discussed. The band gap energies (E(g)) of the obtained alpha-MoO3 nanobelts and MoO2 microaxletrees are calculated to be 2.90 and 3.72 eV, respectively. This work exhibits an effective approach in the selectively controlled synthesis of MoO(x) (x = 2, 3) nanomaterials via one-step hydrothermal strategy.