Single crystalline FeNi3dendrites were successfully synthesized in high yield by a simple and facile hydrothermal method without the presence of surfactants and were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), selected area electron diffraction (SAED), energy dispersive X-ray spectroscopy (EDX), and vibrating sample magnetometer (VSM). The individual FeNi3dendrite consists of a long central trunk with secondary, tertiary, and even quaternary branches. On the dendritic hierarchical structures, several leaves with different lengths of 0.2−2.5 μm and widths of 100 nm to 1 μm are connected to the trunk with a length of 1−5 μm. The reaction parameters such as temperature, the reaction time, the concentration of NaOH, and the initial concentration of Fe3+ions that affected the FeNi3morphology were investigated systematically, based on which possible formation mechanism for the dendrites was proposed. Compared with FeNi3particles, FeNi3dendritic structures exhibited a decreased saturation magnetization (Ms, 61.6 emu/g) but an enhanced coercivity (Hc, 145.6 Oe) due to their peculiar morphology. To our best knowledge, this is the first report on making crystalline metal alloy dendrites with such a full control. [ABSTRACT FROM AUTHOR]