Natural plant extracts / products have the potential as safe alternatives for chemical fungicides in plant disease management. Methanol and pure methanol: water (50:50 v/v) extracts of peppermint, lavandula, eucalyptus, datura and nettle were screened for their antifungal activity against Alternaria sesami, the causal agent of Alternaria leaf spot of sesame at 5, 10 and 15% concentrations in Shahrood Agricultural Research Center, Shahrood, Iran, during 2010. Poisoned food technique and spore germination assay were used to evaluate the antifungal potential of plant extracts against the pathogen. Fungicide mancozeb 80WP (0.2%) was used for better comparison. Results indicated that methanolic extracts of peppermint (15 and 10%), lavandula (15%) and eucalyptus (15%) were more effective than methanol: water extracts and completely inhibited the growth of the pathogen. Among tested extracts, methanolic extracts of peppermint (15%) and eucalyptus (15%) were best in preventing the spore germination of the pathogen (P =0.01).