The electrochemical behavior of metallic palladium nanoparticles obtained by reducing H₂PdCl₄ with formaldehyde and the products of the interaction of H₂PdCl₄ with sodium sulfide with a different ratio of reagents in a solution of hydrochloric acid was studied by the method of cyclic voltammetry. Voltammograms of metallic and sulfide nanoparticles were obtained, and interpretation was given to the observed electrochemical processes. The initial and oxidized systems with different potential values ​​were characterized by X-ray photoelectron spectroscopy (XPS). It is shown that palladium sulfide nanoparticles, obtained at high molar ratios of reagents (S / Pd = 3: 1), are more resistant to oxidative and reducing effects than those obtained at low molar ratios (S / Pd = 1: 1).