Nanocrystalline coatings of Ni-Co were deposited on a carbon steel substrate via electrodeposition by direct current in a Watts-type bath with and without Saccharin addition. The current densities used were 5, 12, 39, 55 and 104 mAcm -2 . The results obtained showed that when Saccharin is added to plating bath, reduces grain size (about half), increases hardness (about twice), changes texture from {311} and {200} to {111} and morphology from pyramidal to smooth. In the absence of saccharin, current density and adsorption of hydrogen complexes and/or intermediate components were distinguished as two effective parameters causing nanocrystalline electrodeposits. In the presence of saccharin, Adsorption of saccharin molecules and/or decomposed sulfide species occurred in saccharin-contained bath, resulted in slow surface diffusion of adions and thus inhibits from grain growth and encourages finer grain structure formation. Tafel polarization test results showed that coatings obtained from with Saccharin bath in spite of those obtained from without Saccharin bath could not form a passive film in 3.5%wt NaCl. EIS test results showed that decreasing the grain size from micro to nanocrstalline doesn't decrease corrosion performance of Ni-Co coating in 10%et NaOH. The tribo-corrosion tests showed that the coating obtained at the higher current density (55 mA cm -2 ) had the same open circuit potential (OCP) before, during and after the sliding wear test. This was attributed to its strong repassivation ability probably provided by its morphology. This behavior was not observed for the coatings deposited at a lower current density (39 mA cm -2 ) or at the presence of sodium luryl sulfate. These coatings showed a lower OCP during and after the sliding wear probably due to the high ratio of active to passive area on their worn region. Adding saccharin into bath resulted in more corrosion rate and change of sliding wear mechanism from abrasive to adhesion. It showed an OCP increase, exceeded than the initial potential, during the sliding wear and a sudden decrease after removing the sliding load. The reason was postulated to be a soluble semi-passive film formation encouraged by the induced structural inflects on the worn area and supported by the presence of the sliding load.