Objective: A new reverse-phase high-performance liquid chromatography (RP-HPLC) method was developed to simultaneously determine curcumin and epigallocatechin gallate (EGCG) in novel nanoformulation. Methods: The high-performance liquid chromatography (HPLC) method was achieved by using a Thermo Scientific Hypersil Base Deactivated Silica (BDS) C18 column (25 cm X 4.6 mm, 5 µm) at 35 °C column oven temperature. The chromatographic procedure was performed with a mobile phase of acetonitrile and 0.025 M (pH 4.0) potassium dihydrogen phosphate (KH2PO4) buffer by gradient mode of elution. The injection volume was 20 µl, and the flow rate was 1.5 ml/min, with ultraviolet (UV) detection using a diode array detector (DAD) at a 268 nm isosbestic wavelength. Results: Drug entrapment efficiency studies were performed with co-encapsulated EGCG and curcumin nanoformulation, which were found to be 94.35 % and 95.12 %, respectively. This shows that the developed method is highly effective. EGCG and curcumin were eluted at 3.9 min and 10.7 min, respectively. The linearity range was 25-175 µg/ml for EGCG and 12.5-100 µg/ml for curcumin. The correlation coefficient was 0.991 for EGCG and 0.999 for curcumin from the linearity curve, which indicates that the method can produce good sensitivity. Forced degradation studies were conducted in acidic, basic, oxidative, thermal, photolytic, and UV stress conditions, where all the degradation peaks were monitored. Conclusion: The developed method was linear, simple, rapid, robust, and precise. It could be used to quantify EGCG and curcumin simultaneously in various nanoformulations for in vivo and in vitro applications.