A　novel　photosensitizer,　pentalysine　beta-carbonyl-phthalocyanine　zinc　[ZnPc-(Lys)(5)]　has　tendency　to　form　aggregate　in　aqueous　solution.　The　observed　in　vivo　Photodynamic　therapy　(PDT)　effect　of　ZnPc-(Lys)(5)　suggests　a　disaggregation　mechanism.　In　this　study,　the　equilibrium　binding　constant　K-a,　the　numbers　of　binding　sites　n　and　the　distance　of　Forster　radii　r　between　ZnPc-(Lys)(5)　and　human　serum　albumin　(HSA)　are　measured　by　Spectroscopy.　A　molecular　model　of　HSA-ZnPc-(Lys)(5)　complex　was　generated　according　to　these　datum.　This　molecular　model　provides　rationale　that　the　molecular　interaction　between　HSA　and　ZnPc-(Lys)(5)　facilitates　the　dissociation　of　ZnPc　aggregates.