The aim of the present study was to evaluate the antifungal activity of fatty acids against phytopathogenic fungi. Two pot experiments were conducted by mixing palmitic and oleic acids in the soil in which poor plant growth was observed. In addition, the antifungal activities of nine fatty acids (butyric acid, caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, oleic acid, and linoleic acid) against four phytopathogenic fungi: Alternaria solani, Colletotrichum lagenarium, Fusarium oxysporum f. sp. Cucumerinum, and Fusarium oxysporum f. sp. lycopersici, were assessed by measuring mycelial growth and spore germination via Petri dish assay. The results of the pot experiments showed that the mixture of palmitic and oleic acids enhanced the growth of the seedlings of continuous-tomato and continuous-cucumber. Except for oleic acid, in the Petri dish assay, the fatty acids tested were observed to inhibit the mycelial growth of one or more tested fungi. In addition to the suppression of mycelial growth, butyric acid, caproic acid, caprylic acid, capric acid, lauric acid, and palmitic acid showed an inhibitory effect against spore germination and the extent of inhibition varied with both the type of fatty acids, and the fungi. In particular, capric acid displayed strong inhibitory effect against C. lagenarium on the mycelial growth and spore germination. The saturated fatty acids, i.e. palmitic acids, showed stronger antifungal activity than the unsaturated fatty acids, i.e. oleic acid. It suggests that fatty acids might be applicable to exploring for alternative approaches to integrated control of phytopathogens.