The kinetics and mechanism of Ag(I)-catalyzed exchange of coordinated cyanide in hexacyanoferrate(H) by D-penicillamine (D-PA) have been monitored by following the appearance of blue colored complex [Fe(CN)(5)(D-PA)](3-) at 423 nm, corresponding to metal to ligand charge transfer (MLCT) transition. The effect ofpH, ionic strength, catalyst concentration and concentration of hexacyanoferrate(H) and D-penicillamine on the rate of reaction has also studied and explained. The findings indicate first order dependence each in [Fe(CN)(6)](4-) and [D-PA]. The composition of the complex formed has been established to be 1:1 by mole ratio and slope ratio method. The kinetic observations suggest that the substitution follows an interchange dissociative (I-d) mechanism which proceeds via formation of a solvent bound intermediate. The activation parameters Delta H-# and Delta S-# have also been calculated and provided in support of the proposed mechanistic scheme. It is observed first time that the drug D-penicillamine used acts as a potential ligand and it can replace the coordinated cyanide in hexacyanoferrate(II).