Water-soluble luminescent material was developed by introducing europium (Eu(III)) ions into the core of a star polymer. Living radical polymerization was used to obtain the star polymer. The strategy to introduce Eu(III) ions into the star polymer was studied using poly(methyl methacrylate) as an arm. The best Eu(III) ion introduction was obtained by simultaneous introduction, resulting in about 30 mu mol/g-polymer, which needed only one step for synthesis. The utilization of a hydrophilic polymer such as poly(ethylene oxide) (PEO) as an arm produced a water-soluble star polymer. The Eu(III)-bearing PEO star polymer obtained in this study was water soluble and showed fluorescence. In addition, it was stable in water after 1 month. The Eu(III)-bearing star polymer exhibited luminescent properties under UV light irradiation with relatively high quantum yields of 60% in organic solution and 19% in aqueous solution. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 25272535