Starting from p-nitrobenzoic acid and p-methoxybenzoic acid, seven new 2-sub-stitutedthio-5- (4-nitro or 4-methoxyphenyl)-1,3,4-thiadiazole compounds 5 were synthesized in five steps including esterification, hydrazidation, salt formation, cyclization and thioetherification. Treatment of 5 with H₂O₂ catalyzed by ammonium molybdate in ethanol afforded the ten 2-substituted sulfonyl-5-(4-nitro or 4-methoxyphenyl)- 1,3,4-thiadiazole 6 with good yields. The structures of the new compounds synthesized were confirmed by ¹H NMR, ¹³C NMR, IR spectra and elemental analysis. The preliminary bioassay showed that compound 5d had good antifungal activity against Fusarium graminearum, Fusarium oxysporum and Cytospora mandshurica with the rate of 99.0%, 100.0% and 100.0% at the concentration of 500 μg•mL^－1, and compound 6j possessed high inhibitory effect with rate of 47.7%, 46.4% and 50.6% at the concentration of 50 μg•mL^－1.

Key words: sulfone, sulfide, 1,3,4-thiadiazole, antifungal activity