Fe3O4 nano-whiskers were synthesized via ultrasonic-aided reduction of FeCl2·4H2O with N2H4·H2O in concentrated NaOH solution. Phase identification and morphology observation were conducted by X-ray diffraction (XRD) analysis,transmission electron microscopy (TEM) and field emission scanning electron microscopy (FE-SEM). Face scanning energy dispersive spectrum (face scanning EDS) and two-dimensional fast Fourier transform (2DFFT) for element distribution were carried out for confirming composition homogeneity. From XRD and TEM,the synthesized Fe3O4 nano-whiskers are of cubic phase with average dimension of 20 nm × 200 nm (average aspect ratio of 10). FE-SEM shows that the nanowhiskers without dispersion are interconnected into a network at a scale of 20μm. 2DFFT of the distribution of Fe and O from face scanning EDS confirms the composition homogeneity of the synthesized Fe3O4. Hydrazine hydrate determines the formation of the nano-whiskers,while the possible mechanism is the preferred growth along certain orientation with the aid of ultrasonic treatment.