Alternaria dauci is the causal agent of Alternaria leaf blight (ALB), a foliar disease of carrot crops (Daucus carota) around the world. In terms of phytotoxic metabolites production, A. dauci has received limited attention. Previous studies carried out on the secondary metabolites involved in the pathogenicity of this fungus have only reported the isolation of a ubiquitous non-selective phytotoxin known as zinniol. Because of this, the aim of this research is directed towards the isolation and identification of secondary metabolites involved in the plant-pathogen interaction process. A. dauci was cultured in the Czapek-Dox medium, and the culture filtrate was extracted with ethyl acetate. The leaf-spot assay of fractions resulting from the partition process showed a phytotoxic effect in the ethyl acetate fraction. The chromatographic separation of ethyl acetate fraction allowed the isolation of seven diketopiperazines, identified as cyclo-(pro-val) (1), cyclo-(pro-leu) (2), cyclo-(pro-phe) (3), cyclo-(val-leu) (4), cyclo-(val-phe) (5), cyclo-(leu-phe) (6) and cyclo-(leu-tyr) (7). The structures of the different metabolites were established by comparing their spectroscopic (H-1 NMR) and spectrometric (GC-MS) data with those reported in the literature.