Two series of compounds namely, dihydroindeno and indeno [1,2-e] [1,2,4]triazolo [3,4-b] [1,3,4]thiadizines (9a-l & 11a-l) were synthesized by cyclocondensation between α-bromoindanones (7a-b) or/and α,α-dibromoindanones (8a-b) and various 3-alkyl/aryl-4-amino-5-mercapto-1,2,4-s-triazoles (3a-f) in methanol with an aim to explore their effect on in vitro growth of microorganism causing microbial infection. In vitro antibacterial activity was performed against four strains namely, Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa and antifungal activity against three fungal strains namely, Aspergillus niger, Aspergillus flavus, Penicillium species. Of all the compounds screened for activity some of the compounds were associated with considerably higher antibacterial and antifungal activity than commercial antibiotics.