Octahedral Fe 4 (PO 4 ) 3 (OH) 3 microcrystals have been successfully prepared by a microwave-assisted hydrothermal route at 170°C for 20min, employing FeCl 3 ·6H 2 O and NaH 2 PO 4 ·2H 2 O as the starting materials in the presence of proper amounts of Na 2 SO 3 and acetic acid (HAc). The phase and morphology of the as-prepared product were characterized by means of powder X-ray diffraction (XRD), energy dispersive spectrometry (EDS), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Some factors influencing the formation of octahedral Fe 4 (PO 4 ) 3 (OH) 3 microcrystals were systematically investigated, including the reaction temperature, time, and the molar ratio of Na 2 SO 3 /HAc.