Acetaldehyde　is　an　essential　commodity　chemical　with　high　demand,　while　its　conventional　production　by　homogeneous　Wacker　oxidation　suffers　from　high　corrosivity,　high　chlorine　by-products,　and　separation　difficulties.　In　this　work,　a　Pd　nanoparticle-loaded　ZnO　(Pd-ZnO)　photocatalyst　is　developed　for　the　selective　oxidation　of　ethylene　to　acetaldehyde.　The　ZnO　substrate　provides　hydroxyl　radicals　(center　dot　OH)　from　water　oxidation,　and　the　Pd　active　sites　allow　to　promote　the　dehydrogenation　of　adsorbed　symmetrical　ethylene　to　form　asymmetrical　vinyl　specie　(*CH2　&　boxH;CH)　with　negatively　charged　carbon,　which　can　be　further　attacked　by　center　dot　OH　to　vinyl　alcohol　(*C2H3OH)　and　finally　undergo　isomerization　to　produce　acetaldehyde　products.　The　Pd-ZnO　photocatalyst　exhibits　a　high　C2H4-to-acetaldehyde　yield　of　＞3500　mu　mol　g(-1)　h(-1)　with　60%　selectivity　at　ambient　temperature　and　pressure　under　illumination　without　the　use　of　sacrificial　agents,　featuring　one　of　the　highest　performances　in　both　photocatalytic　and　electrocatalytic　conversion.　This　work　suggests　an　attractive　opportunity　for　the　photocatalytic　production　of　acetaldehyde　from　ethylene.