2-Phenyl-1-(3?,5?-dichloro-2?-benzo(b)thiophenoylamino)-4-arylidine-5-imidazolones (2a-j) were prepared from the 2-hydrazinocarbonyl-3,5-dichlorobenzo[b]thiophene 1 by the reaction with different oxazolinone which were prepared by the condensation of substituted benzaldehyde with benzoyl glycine in presence of sodium acetate and acetic anhydride. Reaction of 1 with different aromatic isothiocyanate afforded the corresponding N1-(3?,5?-dichlorobenzo[b]thiophen-2?-yl)-N4-substituted aryl thiosemicarbazides (3a-j). Compounds (3a-j) on reaction with sodium hydroxide yielded 3-(3?,5?-dichlorobenzo[b]thiophen-2?-yl)-4-aryl-5-mercapto-1,2,4-triazoles (4a-j). The pharmacological evaluations were performed for their antitubercular and antimicrobial activities. Some novel imidazolones and 1,2,4-triazoles were synthesized and evaluated for in vitro antibacterial activity against Escherichia coli ATCC 25922, Proteus vulgaris ATCC 6380, Bacillus megaterium ATCC 14581, Staphylococcus aureus ATCC 29213, and antifungal activity against Aspergillus niger ATCC 9029. The in vitro antimycobacterial activity of the new compounds was also investigated against Mycobacterium tuberculosis H37RV (ATCC 27294) in BACTEC 12B medium using the ALAMAR radiometric system. The structures of new compounds were supported by IR, 1H-NMR and Mass spectral data.