Polycrystalline CeO2 nanorods 5-10 nm in diameter and 50-150 nm in length were synthesized via ultrasonication using polyethylene glycol (PEG) as a structure-directing agent at room temperature. The properties of the CeO2 nanorods were characterized by TEM, EDS, XRD, XPS, FT-IR, TG, BET, and UV-vis spectroscopy. Various reaction parameters, such as the content of PEG, the molecular weight of PEG, the concentration of KOH, the pH value, and the sonication time, were investigated by a series of control experiments. The content of PEG, the molecular weight of PEG, and the sonication time were confirmed to be the crucial factors determining the formation of one-dimensional CeO2 nanorods. A possible ultrasonic formation mechanism has been suggested to explain the formation of CeO2 nanorods.