The adsorption of carbon monoxide on small alumina-supported Pd particles have been studied by X-ray photoelectron spectroscopy (XPS). The results showed clearly different surface properties of bulk metal and supported clusters. The effect of partial CO dissociation was observed on Pd deposited on gamma-alumina and on clean aluminium, but not on small Pd particles prepared on thin amorphous oxide film on Al substrate. CO-Pd interaction was determined from C 1s photoelectron spectra that exhibited two CO-related components. The dissociation activity was monitored as a rise of C 1s signal at 285 eV, while the molecularly adsorbed CO exhibited the intensity at 287 eV. The study showed that beside the particle size, the metal-substrate interaction (MSI) plays an important role in CO-Pd adsorption process.