A　novel　silicon(IV)　phthalocyanine　(SiPc)　axially　di-substituted　with　Arg-Arg-Arg　oligopeptides　(compound　4)　has　been　synthesized　and　characterized.　Meanwhile,　two　analogues　have　been　used　as　controls.　The　effect　of　arginine　number　on　the　spectral　properties,　photosensitizing　activities,　partition　coefficient,　cellular　uptake,　and　photodynamic　antimicrobial　activities　have　been　investigated.　The　novel　SiPc　4　containing　tri-arginine　oligopeptides　exhibits　an　extremely　high　in　vitro　photodynamic　activity　not　only　against　Gram-positive/negative　bacteria　but　also　against　fungus,　which　is　obviously　superior　to　its　analogues　containing　mono-arginine　(compound　2)　and　di-arginine　oligopeptides　(compound　3).　In　addition,　4　shows　a　higher　photodynamic　inactivation　against　S.aureus,　E.coli　and　C.　albicans　cells　than　methylene　blue　(MB),　a　known　antimicrobial　photosensitizer.　The　IC90　values　against　C.　albicans　for　4　is　ca.　179-fold　lower　than　that　for　MB.　Moreover,　the　potent　photodynamic　effect　of　4　has　been　further　confirmed　by　in　vivo　animal　model.　These　results　indicate　that　the　tri-arginine-modified　SiPc　is　a　highly　promising　photosensitizer　for　photodynamic　antimicrobial　therapy.　©　2019　Elsevier　Ltd