Prussian blue (PB, Fe(III)(4)[Fe(II)(CN)(6)](3)) is a prototype of metal hexacyanoferrates with well-known magnetic properties and electrochromic (redox reaction between Fe2+ and Fe3+) and electrochemical behavior [1,2]. The shape-control of PB has drawn increasing attention owing to its shape-dependent properties such as porosity, storage, and magnetism with stacking order [3]. Wet chemical routes are usually considered a powerful method for top-down shape control by carefully tuning the reaction conditions. However, previous reports focused on chalcogenides, metals, and oxides with selective etching of the special facets of the nanomaterial [3]. In this study, we report a hydrothermal synthesis method to control the shape of monodisperse PB from cube to sphere via selective acid etching. Polyvinylpyrrolidone (PVP), used as a surfactant, not only maintains a good dispersion of the particle without aggregation by stabilizing the PB particles during crystallization but also plays a key role in the etching process after mixing with strong acid. The size and shape of the resulting spherical PB particles were sensitive to the molar concentration of acid solution. Consequently, the spherical PB had a high specific surface area and the calcined PB exhibited superparamagnetic properties. The results show that the spherical PB can be utilized in applications such as magnetic-field-guided drug delivery, cell labeling, and contrast agents for magnetic resonance imaging. The chemical and physical properties of the obtained samples were characterized using X-ray diffraction, Brunauere-Emmette-Teller analysis, Raman spectroscopy, and scanning electron microscopy. (C) 2017 Elsevier B.V. All rights reserved.