Core-imprinted star polymers with precision cavity microgels were designed by living radical polymerization with molecular imprinting for selective molecular recognition. The key is to employ NaI-bearing poly(ethylene glycol) dimethacrylate as a template linker during the linking process of poly(methyl methacrylate) arms with ethylene glycol dimethacrylate; Na-imprinted PEG loop cavities are thus effectively created within microgels. As a result, the star polymer encapsulated NaI 15 times more selectively than KI under competitive conditions.