Abstract: 16SrDNA gene sequence similarity and phylogentic analysis indicated that the strain of antimicrobial activity obtained from soil belonged to the genus Xenorhabdus ehlersii and named Xenorhabdus ehlersii SN22. Xenorhabic acid (compound 1 ) was isolated from fermented broth of X. ehlersii SN22 by silica gel column chromatography and Sephadex LH-20 chromatography. Characterized by X-ray crystal diffraction, ¹HNMR and ¹³C NMR, and ESI-MS spectral analysis, the chemical structure of 1 was confirmed to be 3-(cyclohex-2-en) acrylic acid which was a new natural product. The antifungal activity of Xenorhabic acid against phytopathogenic fungi was determined by mycelium growth rate method. The results showed Xenorhabic acid could effectively inhibit the mycelium growth of Sclerotinia sclerotiorum and Pythium aphanidermatum, and the EC₅₀ values were 27.99 and 29.55 μg/mL respectively. In addition, Xenorhabic acid also showed antibacterial activity against Escherichia coli, with the minimum inhibitory concentration (MIC) value of 62.5 μg/mL.