Citrate complex of nickel has been investigated by pH titration method within the pH range 2.5 to 7. A neutral complex C is formed at lower pH due to the reaction of a nickel ion and citric acid with the simultaneous liberation of two protons. The equilibrium constant of this reaction has been found to be 7.97 x 10-5 This complex with increase in pH dissociates to a H+ ion and complex C1, the dissociation constant being 1.75 x 10-1. At still higher pH the complex C1- farther dissociates like a monobasic acid to C22- and H+. The dissociation constant of the latter reaction is = 35 x 10-5, The structures of these complexes have been discussed.