Interaction between 1-［4-(2-carboxyl-ethyl-)phenoxy］ phthalocyanine Zinc(Ⅱ) (ZnPcC1) and albumin (human serum albumin or bovine serum albumin) was studied.ZnPcC1 can be covalently bound to albumin through amide bond formation.The molar ratios of ZnPcC1 to albumins are found to be about 7∶1 in the covalent bioconjugates.On the other hand, there are strong non-covalent interactions between ZnPcC1 and albumins with a binding constant of ca.1.0×105 mol-1·L.Binding sites competition experiments suggest that the binding site locates in subdomain ⅠB of human serum albumin.When conjugated to albumin, no matter covalent conjugation or non-covalent conjugation, the ZnPcC1 exhibit more distinctive characteristic monomer absorption than the free ZnPcC1, which is a property beneficial to photodynamic therapy.Covalent conjugation results in the Q-band of ZnPcC1 red-shifting about 5 nm, whereas non-covalent conjugation does not lead to red-shift.