Abstract: To synthesize and evaluate antimicrobial activity of novel heterocyclic compounds, the corresponding title aroyl ureas have been synthesized by the reaction of 2-amino-5-(3-pyridyl)-1,3,4-thiadiazole with aroyl isocyanates. Their antimicrobial activities in vitro were tested by disk diffusion methods and broth microdilution according to M-27A protocol recommended by NCCLS. Twelve new compounds were obtained, and their structures were confirmed by MS, IR, ¹H NMR and elemental analysis. The biological screening tests showed that most of the compounds have some antifungal activities in vitro. Aroyl ureas incorporating pyridyl thiadiazole ring may be developed as novel antifungal candidate drugs and are worthwhile to be further studied.