In this study, a simple, rapid and green post-epoxidation treatment for graphene quantum dots (GQDs) was proposed. This method only adjusted epoxy functional groups on GQDs' surface, and correspondingly maintained their original size and concentration. The formation mechanism of this epoxidation of graphene quantum dots (E-GQDs) is similar to the epoxidation of alkenes, which will be epoxidated by electrophilic addition reaction. The GQDs after epoxidation will enhanced surface activity of GQDs, and help to expand its application in biological imaging and photothermal therapy. (C) 2018 Elsevier B.V. All rights reserved.