ABSTRACT. A novel series of antipyrinyl thienyl ketones 4a-c, 7a-c, 10a-c, and 13a-b was chemically synthesized through the cyclocondensation of 4-chloroacetylantipyrine with various 2-substituted-thioacetanilide scaffolds, including 3-arylazo-4-mercapto-4-phenylamino-buten-2-ones, ethyl 2-arylazo-3-mercapto-3-phenylamino-acrylate, 2-cyano-3-mercapto-3-(phenylamino)-N-arylacrylamide, 4-mercapto-4-(phenylamino)but-3-en-2-one, and/or ethyl-3-mercapto-3-(phenylamino)acrylate. Indeed, the reaction of 4-chloroacetylantipyrine with 4-hydroxybenzaldehyde followed by refluxing with 2-cyanoacetohydrazide yielded 2-cyano-N'-(4-(2-(antipyrin-4-yl)-2-oxoethoxy)benzylidene)-acetohydrazide 17 as a building compound, which was used consequentially to synthesize a set of new antipyrinyl thienyl hybrids 19a-d. The chemical structures of newly synthesised compounds were unambiguously confirmed using extensive elemental and spectral data analyses. The newly synthesized compounds were screened for their antioxidant and antimicrobial activities. Compared to the test reference (Ascorbic acid, 88.0%), the antipyrinyl thienyl ketones 13a and 13b substituted with methyl and/or hydroxyl groups at the thiophene ring system displayed excellent antioxidant properties, 87.8% and 87.2%, respectively. Additionally, antipyrinyl thienyl ketones 13a and 13b showed high antibacterial activities, and their relative activity index (which ranges from 68% to 91.7%) was close to that of a reference compound, Ampicillin.   KEY WORDS: 4-Chloroacetylantipyrine, Thioacetanilide, Antipyrinyl thienyl ketones, Antioxidant, Antimicrobial   Bull. Chem. Soc. Ethiop. 2023, 37(1), 123-140.                                                              a DOI:https://dx.doi.org/10.4314/bcse.v37i1.11