(-)-Epigallocatechin-3-O-gallate (EGCG), the most bioactive catechin in green tea, has drawn significant interest as a potent antioxidant and anti-inflammatory compound. However, the application of EGCG has been limited by its rapid autoxidation at physiological pH, which generates cytotoxic levels of reactive oxygen species (ROS). Herein, we report the synthesis of poly(acrylic acid)-EGCG conjugates with tunable degrees of substitution and their spontaneous self-assembly into micellar nanoparticles with enhanced resistance against autoxidation. These nanoparticles not only exhibited superior oxidative stability and cytocompatibility over native EGCG, but also showed excellent ROS-scavenging and anti-inflammatory effects. This work presents a potential strategy to overcome the stability and cytotoxicity issues of EGCG, making it one step closer toward its widespread application.