Abstract: The bioinorganic effect of cadmium ion (Cd2+) on the interaction between micromolecules of 3 flavonids ［i.e., quercetin (Que), hyperin (Hyp) and rutin (Rut)］ and bovine serum albumin (BSA) was studied by fluorospectrometry and UV-spectrophotometry. The parameters including the binding constants, number of binding sites, binding force and protein conformation in the absence and presence of Cd2+ were studied comparatively. It was found that the binding sites between Cd2+ and Hyp (or Rut) were located at its glucosyl group, and the Cd2+ was found to take part directly in the binding of the 2 flavonoids with BSA by acting as an “ion bridge”, thus making it favorable for both of the 2 flavonoids to insert into the hydrophobic cavity of the protein. But-off group sited at 3 of the carbon ring of mother nucleus of Que was found not favorable for such “ion bridge” action. It was proved that the “ion bridge” was the main participation mechanism for Cd2+ in the course of interaction between the micromolecules of the flavonoids and BSA.