Electrodeposition of nanocrystalline Ni and Ni1-xCox thin films from chloride baths was systematically investigated by varying the electrodeposition parameters including electrolyte composition (i.e., Co2+ ion concentration), additive (i.e., saccharin), solution pH, and current density. Their effects on the film growth mechanism, film composition, residual stress, microstructure, grain size, and surface morphology were studied. Ni1-xCox thin films electrodeposited from the baths without the addition of saccharin always showed tensile stress mode (145-367 MPa) with varying Co2+ ion concentration, solution pH, and current density. In the presence of saccharin, the Ni1-xCox thin films showed either tensile stress or compressive stress mode, depending on the electrodeposition conditions. Especially, it was observed from a cross-sectional TEM observation that Ni thin film electrodeposited from the bath containing saccharin exhibited the formation of an amorphous Ni layer (about 300 nm thick) at the initial stage of the film growth. Also, Ni1-xCox thin films electrodeposited from the bath with/without the addition of saccharin showed the formation of the interface phase layer (about 10-110 nm thick), which has the chemical composition of 50 atom % Ni and 50 atom % Co. (c) 2006 The Electrochemical Society.