In this article, water-dispersible Ag2Se quantum dots (QDs) were prepared by the facile and environmental-friendly method. In our approach, atom transfer radical polymerization (ATRP) was adopted in aqueous media to grow polymer chains from the surface of Ag2Se QDs. The aqueous ATRP allows the very mild synthetic conditions. In the present work, the polymerization reaction of methoxy[oligo(ethylene glycol)] methacrylate (OEGMA) was carried out at room temperature under aqueous conditions after the incorporation of 2-bromopropionyl moiety as the ATRP initiator on the surface of Ag2Se QDs by the ligand exchange method. OEGMA-coated Ag2Se QDs were successfully obtained without significant morphological change. The aqueous dispersion stability of OEGMA-coated Ag2Se QDs was compared with that of conventional water-dispersible Ag2Se QDs prepared by the simple modification with 11-mercaptoundecanoic acid. As a result, OEGMA-coated Ag2Se QDs showed the extremely high aqueous dispersion stability.