Three important low valent transition metal oxides were synthesized in supercritical methanol by using inorganic metal salts as precursors. X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, and x-ray photoelectron spectroscopy were applied to analyze the composition, structure, and morphology of the products. Results showed that Cu2O, MoO2, and V2O3 were obtained successfully under a supercritical condition of 240 °C and 9.0 MPa. MoO2 and V2O3 displayed sphere-like morphology with average particle sizes of 20–40 and 20–50 nm, respectively. Cu2O particles displayed edge-truncated cubic morphology with a particle size of 2.5 μm. Formation mechanism proposed that high valent metal oxides (CuO, MoO3, and V2O5) were formed firstly in supercritical methanol by the decomposing of precursors and then reduced to target products by free hydroxyl anions. In addition, methanol performed important roles not only as a reaction medium but also as a reducing agent under supercritical fluid conditions.