Forages generally suffer more severe nutrition stress than other crops,but the corresponding theoretical studies still lag behind. In this study,metabolites in tall fescue leaves under normal and low nitrogen conditions were analyzed with LC-ESI-MS( liquid chromatography-electrospray ionization-mass spectrometry). A total of 1 424 and 1 251 metabolites were detected from two groups of samples respectively using OPLS-DA( orthogonal partial least squares discriminant analysis). The content of 13 major metabolites changed under low nitrogen stress,including auxin( indole acetic acid,IAA). Quantitative real-time PCR( qRTPCR) showed that eight genes related to IAA signaling pathway were up-regulated after nitrogen stress. Enzyme-linked immuno sorbent assay( ELISA) revealed that the IAA concentration was elevated in tall fescue leaves after nitrogen stress. Our research provides valuable information for studying the response mechanisms of tall fescue to low nitrogen. The results suggest that application of IAA could be used to alleviate the harmful effects of nitrogen deficiency. In this study, metabolites in tall fescue leaves under normal and low nitrogen conditions were analyzed with LC-ESI-MS (liquid chromatography-electrospray ionization- A total of 1 424 and 1 251 metabolites were detected from two groups of samples respectively using OPLS-DA (orthogonal partial least squares discriminant analysis). The content of 13 major metabolites changed under low nitrogen stress, including auxin (indole acetic acid, IAA). Quantitative real-time PCR (qRTPCR) showed that eight genes related to IAA signaling pathway were up-regulated after nitrogen stress. Enzyme-linked immuno sorbent assay (ELISA) revealed that the IAA concentration was elevated in tall fescue leaves after nitrogen stress. Our research provides valuable information for studying the response mechanisms of tall fescue to low nitrogen. The results suggest that application of IAA could be used to alleviate the harmful effects of nitrogen deficiency.