Zinc　phthalocyanine　(ZnPc)　is　a　promising　photosensitizer　for　photodynamic　therapy,　but　faces　some　challenges:　ZnPc　is　insoluble　in　water　and　thus　requires　either　special　formulation　of　ZnPc　by,　e.g.,　liposome　or　Cremophor　EL,　or　chemical　modification　of　Pc　ring　to　enhance　its　bioavailability　and　photodynamic　efficacy.　Here,　we　conjugated　monosubstituted　ZnPc-COOH　with　a　series　of　oligolysine　moieties　with　different　numbers　of　lysine　residues　(ZnPc-(Lys)(n)　(n　=　1,　3,　5,　7,　9)　to　improve　the　water　solubility　of　the　ZnPc　conjugates.　We　measured　the　photosensitizing　efficacies　and　the　cellular　uptakes　of　this　series　of　conjugates　on　a　normal　and　a　cancerous　cell　line.　In　addition,　we　developed　a　sensitive　in　situ　method　to　distinguish　the　difference　in　photodynamic　efficacy　among　conjugates　Our　results　showed　that　ZnPc-(Lys)(7)　has　the　highest　photodynamic　efficacy　compared　to　the　other　conjugates　investigated.