This　study　concerned　the　effects　of　Di　(2-ethylhexyl)　phthalate　(DEHP)　on　two　kinds　of　duckweeds　(Spirodela　polyrhiza　and　Lemna　minor).　The　results　indicated　that　DEHP　has　aquatic　toxicity　to　Spirodela　polyrhiza　at　0.4　mg/L　and　to　Lemna　minor　at　over　0.1　mg/L　by　changing　their　physiologic-biochemical　characteristics.　The　contents　of　duckweed　chlorophyll　and　soluble　protein　decreased　with　DEHP　concentration　increasing　after　7　d　of　exposure.　DEEP　showed　the　stimulating　role　in　catalase　(CAT)　and　superoxide　dismutase　(SOD)　systems　at　relative　low　levels.　At　0.01　mg/L　and　0.005　mg/L,　SOD　activities　of　Spirodela　polyrhiza　and　Lemna　minor　reached　peak　value　respectively,　while　CAT　activity　reached　maximum　value　at　0.05　mg/L　and　0.01　mg/L.　When　DEHP　levels　were　too　high,　the　protection　enzyme　system　would　be　destroyed　and　plant　growth　would　be　inhibited.　The　analysis　of　malondialdehyde　(MDA)　and　Fourier　transform　infrared　spectroscopy　manifested　that　DEHP　could　affect　the　tested　duckweeds　by　destroying　its　cell　membranes,　and　Spirodela　polyrhiza　is　more　resistant　to　DEHP　exposure　than　Lemna　minor.