Considering　that　cancer　has　become　the　second　leading　cause　of　death　in　humans,　it　is　essential　to　develop　an　analytical　approach　that　can　sensitively　detect　tumor　markers　for　early　detection.　We　report　an　attenuated　photoelectrochemical　(PEC)　immunoassay　based　on　the　organic-inorganic　heterojunction　10MIL-88B(FeV)/　ZnIn2S4　(10M88B(FeV)/ZIS)　as　a　photoactive　material　for　monitoring　carcinoembryonic　antigen　(CEA).　The　10M88B(FeV)/ZIS　heterojunctions　have　excellent　light-harvesting　properties　and　high　electrical　conductivity,　which　are　attributed　to　the　advantages　of　both　organic　and　inorganic　semiconductors,　namely,　remarkable　photogenerated　carrier　separation　efficiency　and　long　photogenerated　carrier　lifetime.　Horseradish　peroxidase　(HRP)　in　the　presence　of　H2O2　can　catalyze　3,3　＇-diaminofenamide　(DAB)　producing　brown　precipitates　(oxDAB),　which　is　then　loaded　onto　the　10M88B(FeV)/ZIS　heterojunction　to　reduce　the　photocurrent　and　enable　the　quantitative　detection　of　CEA.　Under　optimal　conditions,　the　photocurrent　values　of　the　PEC　biosensor　are　linearly　related　to　the　logarithm　of　the　CEA　concentrations,　ranging　from　0.01　ng　mL-1　to　100　ng　mL-1　with　a　detection　limit　(LOD)　of　4.0　pg　mL-1.　Notably,　the　accuracy　of　the　PEC　biosensor　is　in　agreement　with　that　of　the　human　CEA　enzyme-linked　immunosorbent　assay　(ELISA)　kit.