1, 3, 4- thiadiazoles are potential bioactive agents having the toxophoric N=C__ampersandsignndash;S linkage. There are several isomers of thiadiazole, i.e.1,2,3-thiadiazole, 1,2,4-thiadiazole, 1,2,5-thiadiazole, and 1,3,4-thiadiazole. However 1, 3, 4-Thiadiazole is the main isomer of the thiadiazole series which has versatile pharmacological activities. Hence in this study we have synthesized some new substituted 1, 3, 4 thiadiazoles i.e. N-phthalyl-[{(3-nitro anilino)-4__ampersandsignrsquo;__ampersandsignrsquo; aryl Substituted}]-1, 3, 4 thiadiazoles. The title compounds were prepared from N-phthayl-3-nitro anilino thiosemicarbazide by treating N-phthayl-3-nitro aniline with carbon disulphide, ammonium hydroxide and hydrazine hydrate. The synthesized compounds were then evaluated for their in- vitro antioxidant activity by determining the reducing power and hydrogen peroxide scavenging potential. The results show that one derivative V2 (N-Phthalyl-[{(3__ampersandsignrsquo;-nitro anilino)-5-(4__ampersandsignrsquo;__ampersandsignrsquo;-chloro phenyl)}]-1, 3, 4-thiadiazole) had the best redusing ability while V4 (N-Phthalyl-[{(3__ampersandsignrsquo;- nitro anilino)-5- (4__ampersandsignrsquo;__ampersandsignrsquo;-bromo phenyl)}]-1, 3, 4-thiadiazole) was the strongest oxidant. The chemical structures of the synthesized compounds have been characterized by IR, 1HNMR and mass spectra.