Some novel 2-(5-substituted-3-phenyl-1H-indol-2-yl)-5-methyl / phenyl-7H-[1,3,4] oxadiazolo / thiadiazolo [3,2- a][1,3,5]triazine-7-thiones (6&7a-f) were prepared from the intra molecular cyclocondensation of N-((5-(5- substituted-3-phenyl-1H-indol-2-yl)-1,3,4-oxadiazol / thiadiazol-2-yl)carbamothioyl)acetamides / benzamides (4& 5a-f). Which were occurred from the condensation of 5-(5-substituted-3-phenyl-1H-indol-2-yl)-1,3,4-oxadiazol / thiadiazol-2-amine (2&3a-c) with acetyl and benzoyl chlorides in the presence of ammonium thiocynate. The compounds 2a-c & 3a-c were obtained from base and acid catalyzed cyclisation reactions of 2-(5-substituted-3- phenyl-1H-indole-2-carbonyl) hydrazine carbothioamides (1a-c) in ethanol. The compounds synthesized were characterized by using their spectral (IR, NMR and Mass) and analytical studies. All synthesized molecules are evaluated to in-vitro antimicrobial activities against various microbial strains. Most of the new molecules are displayed moderate to significant activities towards antibacterial and antifungal strains.