The main objective of this study is to evaluate addition of some antioxidants to diniconazole fungicide on the three isolated fungi, i.e., Alternaria alternata, Fusarium graminearum and Pyrenophora tritici-repentis. Three antioxidants, i.e., selenium at 5ppm, butylated hydroxyanisole at 50ppm and ascorbic acid at 100ppm were combined with different concentrations of diniconazole, 0.1, 0.5, 1, 3 and 5ppm, in Potato Dextrose Broth (PDB) medium. The vital ingredients, i.e., fresh weight, total carbohydrates, lipids and proteins of the fungi were determined. The results clearly indicated that fungicide-antioxidant mixtures decreased the vital ingredients of the tested fungimore effectively than the fungicide or antioxidants applied alone. Regardless the isolated fungi, the percent reduction of any of the vital ingredients followed the order; Se < BHA < AsA. These effects increased with increasing the concentration of the fungicide in culture medium. This means that antioxidants, especially selenium, enhanced the fungitoxic activity of diniconazole against the isolated fungi.