4-Amino-5-phenyl-4H-1,2,4-triazole-3-thiol (1) underwent facile condensation with various phosphorus dichlorides (2a—j) in the presence of triethylamine in dry tetrahydrofuran at 60—65 °C and afforded corresponding thiadiazaphosphol-2-ones (3a—j). Their chemical structures were characterized using IR, 1H-, 13C-, 31P-NMR and Mass spectral studies. All the title compounds were screened for antioxidant properties by radical scavenging methods such as 1,1-diphenyl-2-picryl hydrazyl (DPPH), hydroxyl and lipid peroxidation. They exhibited potent in vitro antioxidant activity dose dependently. Their bioassay showed them to possess significant antibacterial activity.