Abstract: The protective effects of nitric oxide on small deckweed response to UV-B radiated were studied in this paper.The chlorophyll content of the deckweed dropped down,nitric oxide prevent the process.The dissolubility protein was reduced by UV-B radiated,nitric oxide protect the protein demolished by UVB.The SOD 、POD and CAT raised treated with UV-B,nitric oxide also boosted the activities of SOD 、 POD and CAT.The results suggested that nitric oxide enhanced competence of the plant response to UV-B radiance.