Bi- and monometallic nanoparticles of Au and Pd with a rather narrow size distribution were deposited on polyaniline (PANI) and their structural properties as well as catalytic behavior in the aerobic oxidation of benzyl alcohol were investigated. The size of the mono- and bimetallic particles was controlled in a narrow range (2.4−3.7 nm) using a colloidal preparation route. Admixing Pd to Au resulted in a strong enhancement of selectivity to benzaldehyde reaching a maximum of 98% at full conversion at 100 °C with bimetallic particles containing Au/Pd in a ratio of 1:9. Pure Au particles were significantly more active than pure palladium particles of the same size. Chemical, structural, and electronic properties of the bimetallic catalysts were characterized using high angle annular dark field scanning transmission electron microscopy, atomic absorption spectroscopy, X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy. The PANI-supported nanoparticles showed a core shell structure wi...