Polymeric micelles with a polystyrene (PS) shell and a protonated poly(4-vinylpyridine) (P4VP)/ water core were readily prepared via diffusion of HCl and water from the top aqueous phase containing HCl (pH = 1) into the bottom phase of the PS-b-P4VP solution in chloroform. The resultant protonation of the pyridine units of the P4VP block drove the micellization. Meanwhile, due to the high polarity of the core, water molecules also diffused through the chloroform medium into the core. H-1 NMR characterizations demonstrate that at the early stage, the water molecules in the core are the bound and intermediate water; longer diffusion times resulted in the appearance of free water molecules coexisting with the bound and intermediate water in the core. Thus, polymeric micelles with an aqueous core (PMACs) were formed. The process of forming PMACs is well-control] able, and the stability of PMACs in chloroform is high. These characteristics make PMACs promising as nanoreactors to prepare inorganic nanoparticles or for other applications based on the nanosized aqueous core. Similar to reverse mini- and microemulsion systems, the same PMACs can load a large variety of water-soluble inorganic species and be used to prepare various inorganic nanoparticles within the core. Meanwhile, similar to block copolymer micelles, the soluble shell of PMACs can provide a good solubility for the inorganic nanoparticles formed in the core. Therefore, when used as nanoreactors to prepare inorganic nanoparticles, PMACs can combine the advantages of reverse emulsion systems and polymeric micelles dispersed in a low polar solvent. Herein, PMACs with a PS shell and a protonated P4VP/water core prepared in chloroform were used as nanoreactors to prepare various inorganic nanoparticles, such as silica, Fe(SCN)(2+), AgCl, and Ag2CINO3. The formed inorganic nanoparticles were encapsulated in the core and stabilized in chloroform by the soluble PS shell.