Non-spherical structured nanoparticles have drawn much attention for various applications because they have more complicated structure and properties than simple spherical nanoparticles and can show development possibility as fresh nano-reactors. Among them, silica nanoparticles with open cavity such as concave or bowl nanoparticles can be used as promising reactor in catalyst, delivery carrier and biosensor. In this research, we synthesized bowl structured silica nanoparticles with Fe₃O₄ in about 50nm diameter scale using Janus Fe₃O₄@SiO₂ nanoparticles. After chemical etching in acidic solution at room temperature, each nanoparticle has cavity and finally bowl-shaped structure was obtained. Up to date, concave silica nanoparticles having a size of several hundred nanometers have been reported and this size is limited in practical applications. Because they have unique physiochemical properties; very stable in aqueous solution and functionalized with Fe₃O₄ and amine functional group from aminosilane. So we can expect that these functionalized silica nanoparticles can be used in broad applications.