In the present investigation, a series of novel 2-(4-methoxy-phenyl)-5-methyl-4-(2-arylsulfanyl-ethyl)-2,4-dihydro-[1,2,4] triazolo-3-ones and their corresponding sulfones were prepared with the objective of developing better antimicrobial agents. The chemical structures of the newly synthesized compounds were characterized by spectral (IR, (1)H NMR, (13)C NMR and LCMS) methods. The newly synthesized compounds (4a-i) and (5a-e, 5h) were screened for their antimicrobial activity against Bacillus subtilis, Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli and Pseudomonas aeruginosa. The antifungal activity was tested against Rhizopus oryzae, Aspergillus niger, Aspergillus flavus, Candida albicans and Saccharomyces cerevisiae. Among all the compounds synthesized, compounds 4d and 5b exhibited significant antibacterial activity.