In this study, sub-microsized CoFe 2 O 4 octahedra with a high yield are synthesized via a simple hydrothermal route under mild conditions. The as-prepared products are characterized by conventional techniques of XRD, SEM, TEM, ED and HR-TEM. The results show that the as-synthesized sample exhibits octahedral morphology with a narrow size distribution. The edge size of CoFe 2 O 4 octahedra is estimated to be about 0.10-0.14 mm. The growth process is also monitored by time and temperature-dependent observation. It is found that the reaction temperature has no obvious influence on the product morphology but a significant effect on the size of CoFe 2 O 4 octahedra, while the reaction time determines the final morphology of the product. Moreover, it is displayed that the citrate ions play a key role in the formation of CoFe 2 O 4 octahedra. Furthermore, the possible growth mechanism of the sub-microsized CoFe 2 O 4 octahedra is discussed on the basis of a series of experiments. Magnetic measurements show that sub-micro-sized CoFe 2 O 4 octahedra exhibit obvious ferromagnetic behaviors. The saturation magnetization (M s ), remanent magnetization (M r ), and coercivity (H c ) are determined to be 85.8, 29.2 emu/g and 892 Oe, respectively.