Epigallocatechin gallate (EGCG), an important active component extracted from green tea, has attracted much attention due to its multiple biological activities such as antioxidant, antibacterial, anti-inflammatory, and antitumor effects. Meanwhile, metformin (Met), a classic drug for the treatment of type 2 diabetes, exhibits additional benefits such as hypoglycemic, antioxidant, anti-inflammatory, and antitumor effects. However, metformin often causes gastrointestinal reactions when used alone, affecting patients' quality of life. In view of this, we proposed an innovative technique for the fabrication of a carrier-free, dual-loaded nanodrug, Met-EGCG nanoparticles (Met-EGCG NPs), via self-assembly. The method for preparing Met-EGCG NPs is simple, rapid and cost-effective. In addition, the carrier-free Met-EGCG NPs nanodrug inherits the strong antioxidant capacity, good biocompatibility and excellent aggregation-induced fluorescence effect of EGCG, and even offer significant advantages in enhancing drug solubility, stability, and bioavailability, while effectively reducing the occurrence of side effects. Moreover, this Met-EGCG NPs nanodrug exhibits a synergistic therapeutic effect of EGCG and metformin, thereby significantly enhancing overall therapeutic efficacy, and demonstrates excellent potential in anti-cancer applications. This study not only successfully prepared Met-EGCG NPs but also experimentally verified their superior performance, opening a new path for the application of EGCG in drug therapy. This carrier-free, dual-loaded drug delivery nanosystem based on Met-EGCG NPs offers potential for drug combination therapy, promising to play a more critical role in the biomedical field and providing new insights and guidance for the development of future multidrug delivery systems.