Different sizes of icosahedral-like dendrimer-encapsulated Au nanoparticles (Au-55- and Au-147-DENs) were prepared in the presence of generation 6 amine-terminated dendrimers (G6-PAMAM-NH2) as a template. The synthesis is carried out by the complexation of a Au metal precursor (AuHCI4) with the tertiary amine groups within the dendrimer framework. The addition of excess reducing agent, NaBH4, results in the formation of Au nanoparticles encapsulated within the dendrimer cavities. The as-prepared catalysts were characterized using UV-visible (UV-vis) spectroscopy, high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray analysis (EDX), and Fourier transform infrared (FTIR). The average sizes of Au-55- and Au-147-DENs were determined to be 1.7 +/- 0.4 and 2.0 +/- 0.3 mu, respectively. The catalytic activity of these Au-DEN catalysts was evaluated in the oxidative decomposition of morin by H2O2. Since morin has a maximum absorption band at lambda 410 mu at pH 10, this catalyzed oxidation process was monitored by time-resolved UV-vis spectroscopy. The catalytic activities of these two catalysts were compared by fitting the kinetic data to the Langmuir-Hinshelwood model. This model allows the determination of adsorption constants of both morin (K-morin) and H2O2 (K-H2O2) on the catalyst surface. A full kinetic study for this Au-DEN-catalyzed oxidative degradation of morin is reported.