Dendritic magnetite crystals were fabricated by a surfactant-assisted hydrothermal method. The phase purity and composition of the dendrites were characterized by Mössbauer spectroscopy and X-ray diffraction (XRD), respectively. The morphology of the dendrites was measured by scanning electron microscopy (SEM) images. The oriented growth direction of the dendrites was determined by transmission electron microscopy (TEM) and selection area electron diffraction (SAED). The results showed that the products were pure magnetite crystals consisting of dendritic structures. Each dendrite was mainly composed of one trunk and four groups of branches. The trunk grew along [110] with two pairs of 111-oriented branches grown on the trunk perpendicularly. The shape of the crystals strongly depended on the concentration of K3[Fe(CN)6], concentration of cetyltrimethylammonium bromide (CTAB), hydrothermal temperature, and type of surfactant. With the use of mixed surfactant chain-like particles could be obtained. Fourier transform infrared spectrum (FT-IR) showed CTAB adsorbed on the surface of dendritc magnetite strongly. A slow oriented growth mechanism was put forward to explain formation of dendrites. The slow dissociation of K3[Fe(CN)6] should be responsible for the slow growth rate of the crystals. Adsorption of CTAB on the surface of the magnetite crystals led to oriented growth of the dendritic microcrystals.