Since　the　discovery　of　photodynamic　therapy,　scientists　have　constantly　been　searching　for　more　effective　and　ideal　photosensitizers　(PSs).　As　part　of　our　ongoing　interest　in　the　development　of　more　potent　photosensitizers,　quinoline-8-yloxy-substituted　zinc(II)　phthalocyanine　(ZnPc-Q1)　has　been　identified　as　a　promising　photosensitizers　in　tumor　cells.　This　study　aims　to　explore　the　photodynamic　mechanism　and　in　vivo　photodynamic　efficacy　of　ZnPc-Q1,　and　further　evaluate　its　potential　in　clinical　photodynamic　therapy　application.　The　single　crystal　structure　of　ZnPc-Q1　enables　the　easy　control　of　clinical　quality　standards.　In　comparison　with　Photofrin,　ZnPc-Q1　exhibits　considerably　higher　in　vitro　anticancer　activity　by　dual　dose-related　mechanisms　(antiproliferative　and　apoptosis).　In　addition,　the　in　vivo　results　demonstrate　that　ZnPc-Q1　exhibits　significant　tumor　regression　with　less　skin　photosensitivity　by　both　direct　killing　and　apoptosis　anticancer　mechanisms.　In　conclusion,　ZnPc-Q1　can　be　considered　to　be　a　promising　ideal　PS　for　clinical　application　owing　to　its　defined　chemical　structure　without　phthalocyanine　isomerization,　good　absorption　of　tissue-penetrating　red　light,　improved　photodynamic　therapy　efficacy,　and　reduced　skin　phototoxicity.　(C)　2020　Optical　Society　of　America　under　the　terms　of　the　OSA　Open　Access　Publishing　Agreement