ABSTRACTIn continuing our efforts to find new effective antimicrobial agents for overcoming the problem of microbial resistance, a new series of functionalized 5-hetarylthiazoles have been designed and synthesized starting from readily accessible 1-(2-allylamino-4-methylthiazol-5-yl)ethanone (3). The structures of newly synthesized compounds were confirmed by elemental analyses, spectral data, and chemical transformations. The synthesized compounds were evaluated in vitro for their antimicrobial activity against some human pathogenic bacterial and fungal strains. The compounds 7, 18, and 24 exhibited higher antibacterial activity with minimum inhibitory concentration (MIC) values ranging from (0.03–0.06 µg/mL) than ampicillin (MIC, 0.12 µg/mL) against Streptococcus pneumoniae. Whereas compounds 4, 22, and 24 revealed higher antifungal potency than amphotericin B against Aspergillus fumigatus. The structure and antimicrobial activity relationship was also discussed.