Abstract: Based on thermodynamic speciation calculations, the roles of complexing agents in electroless nickel solutions, employed in ohemic electrodes formation of BaTiO₃-based PTCR ceramics, were investigated in this paper. Electroless nickel solutions, using acetate or citrate or glycine, decrease the concentration of free nickel. All solutions exhibit a fraction of free nickel, which would be decreased with the formation constant of the nickel-ligand species increased. The plating rate and solution stability are dependent upon the structure of nickel in solution. Higher deposition rates were observed in nickel solutions with fewer chelated sites in the nickel complex.