The　di-sulfo,　di-phthalimidomethyl-zinc　phthalolcyanine　(ZnPcS　2P2),　which　has　the　photodynamic　activities　against　tumors　as　amphiphilic　photosensitizer　for　photodynamic　therapy,　is　transported　by　the　blood　circulatory　system　to　target　tissues.　In　this　paper,　the　interaction　of　phthalocyanine　with　bovine　serum　albumin　(BSA)　has　been　investigated　using　absorption　and　differential　absorption　spectra,　steady-state　and　time-resolved　fluorescence　spectra　as　well　as　equilibrium　dialysis.　The　results　show　that　ZnPcS2P2　molecules　are　combined　to　BSA　mainly　in　monomer　fashion.　Addition　of　ZnPcS2P2　results　in　the　conformational　changes　of　BSA.　Based　on　the　Hill　plot　model,　an　improving　method　of　quenching　albumin　intrinsic　tryptophan　fluorescence,　which　supported　the　cooperative　binding　of　ZnPcS2P2　with　BSA,　was　applied.　ZnPcS2P2　occupies　one　strong　binding　site　and　four　weaker　sites,　the　binding　constant　K　is　3.2　×　105　L/mol　and　2.0　×　105　L/mol　respectively.　The　binding　constants　are　consistent　with　those　obtained　by　equilibrium　dialysis.