A series of 5-(2-hydroxyphenyl)-1,3,4-thiadiazol-2-yl-sulfanyl acetyl hydrazones were synthesized with 2-mercapto-5-(2-hydroxyphenyl)-1,3,4-thiadiazole as starting material, followed by thioetherification, hydrazide reaction and hydrazone reaction. The structures of these compounds were characterized by 1 H NMR, 13 C NMR, IR, MS techniques and elemental analysis. The antimicrobial activities of these compounds were also originally studied. The results showed that most of these compounds have potent antibacterial activities. These compounds of aromatic aldehyde-5-(2-hydroxyphen-yl)-1,3,4-thiadiazol-2-yl-sulfanyl acetyl hydrazone (4a~4h) showed better antibacterial activities than 2-butenal-5-(2-hydroxyphenyl)-1,3,4-thiadiazol-2-yl-sulfanyl acetyl hydrazone (4i).