A role of anions in potentiostatic electrodeposition of cobalt from acidic gluconate solutions was investigated. Equilibrium distribution of soluble species in the solutions was calculated and compared with absorption spectra. Cyclic voltammetry and potentiostatic measurements confirmed that cathodic process was inhibited mainly by free sulfate ions. Improved buffer capacity of gluconate baths by addition of sulfate ions protected against contamination of metal deposits by products of cobalt salt hydrolysis. Mathematical models of metal nucleation were tested indicating progressive mode responsible for the formation of the metal phase. Diffusion coefficients of cobalt species were also calculated using various approaches. Thickness, morphology and structure of cobalt deposits as well as cathodic current efficiency were also discussed.