The electrocatalytic behavior of glassy carbon (GC) electrode modified with ruthenium nanoparticles and ruthenium film was studied for electrochemical reduction of nicotinamide adenine dinucleotide (NAD(+)). The surface of GC electrode was modified via cathodic deposition of nanosized ruthenium at different potentials. Scanning electron microscopy (SEM) images showed two kinds of surface morphologies based on deposition potential: Ru nanoparticles-decorated GC at -0.3 V and Ru film-coated GC at -0.5 V versus Ag/AgCl. The electrochemical behavior of Ru nanoparticles and Ru film-modified GC electrodes in phosphate buffer solution containing NAD(+) was investigated using voltammetric techniques. A prominent cathodic peak was observed on bare GC and Ru nanoparticles-modified GC at -1.2 V versus Ag/AgCl which was related to NAD(+) reduction. The electrochemical response of Ru film electrode was reversible, exhibiting a reduction peak at ca. -1.0 V and an oxidation peak at ca. -0.55 V which was attributed mainly to the hydrogen evolution reaction. Electrochemical impedance analysis indicated lower charge transfer resistance of Ru film electrode for hydrogen evolution as compared to GC and Ru nanoparticle electrodes. Ru film-modified electrode was found less reactive than the nanoparticles-modified GC electrode for NAD(+) reduction reaction due to hydrogen evolution reaction that proceeds exclusively on Ru film.