tVery small platinum nanoclusters have been synthesized by reduction of H2PtCl6·6H2O salt with NaBH4in the presence and absence of water-soluble l-cysteine ligand. The synthesized platinum clusters weresupported over anatase titanium dioxide (TiO2) by 1% wt/wt. The spectroscopic properties of Ptn(l-Cys)mclusters were studied by UV–vis spectroscopy and Fourier transform infrared spectroscopy (FTIR) andits chemical structure were determined by thermogravimetric analysis (TGA) and elemental analysis.The particle sizes of supported and non-supported platinum clusters were characterized by transmis-sion electron microscopy (TEM) and powder X-ray diffraction analysis. As well as their specific surfaceareas were determined using nitrogen adsorption/desorption measurements, pore volume and averagepore diameter were also calculated. Finally, oxidation of styrene is used as a simple model reaction todemonstrate that these systems exhibit the potential to be used as heterogeneous catalysts. The dopedmonodisperse platinum clusters (1% Ptn(l-Cys)m/TiO2) catalyst exhibited the highest catalytic activityand selectivity (100% benzaldehyde) in oxidation of styrene. The non-doped platinum clusters (Ptn(l-Cys)m) showed more catalytic activity than doped polydisperse platinum clusters (1% Pt/TiO2). Hydrogenperoxide was used as oxidizing agent, which exhibited stronger oxidation potential than oxygen gas.The unique atom-packing structure and electronic properties of Ptn(l-Cys)mnanoclusters (∼1 nm) arerationalized to be responsible for their extraordinary catalytic activity observed in oxidation of styrene.