In this study, the AuNPs synthesized from the extract of Phlogacanthus turgidus exhibited absorption peaks within the wavelength range of 500 nm to 600 nm. The results of TEM and SEM showed that the structure of AuNPs exhibits various shapes, including cylindrical, spherical, and polygonal forms. Additionally, clusters of AuNPs were observed with different sizes. Various factors affecting the redox reaction between hydrogen peroxide (H2O2) and 3,3',5,5'-Tetramethylbenzidine (TMB) using AuNPs as a catalyst were investigated. These factors included temperature, reaction time, pH, the amount of AuNPs, TMB concentration, and H2O2concentration. UV-Vis spectrophotometry was utilized to determine the optimal conditions for H2O2detection through the ox-TMB color reaction with the AuNPs catalyst, thereby evaluating their applicability as H2O2 sensors.