Titrimetric analysis of solutions of nickel(II) chloride and citric acid, H
L, has led to the characterization of four complexes in the acidic pH range NiL
, NiHL, NiH
, and Nil
. Equilibrium constants for the formation of these complexes are reported. Results from a visible spectrophotometric study are analysed in terms of these four complexes. The stability and possible structures of the complexes are discussed and compared with other nickel-carboxylic acid complexes.