N'-(3,4-Diarylthiazol-2(3H)-ylidene)-2-(arylthio)acetohydrazides were synthesized and evaluated for their antimicrobial activity and cytotoxicity against NIH/3T3 cells. Compound 22 bearing 1-phenyl-1H-tetrazole and p-chlorophenyl moieties was found to be the most promising antibacterial agent against Pseudomonas aeruginosa, whereas compound 23 bearing 1-phenyl-1H-tetrazole and p-bromophenyl moieties was the most promising antifungal agent against Candida albicans. The most effective derivatives were also evaluated for their cytotoxicity against C6 glioma cells. The results indicated that compound 17 bearing 1-phenyl-1H-tetrazole and nonsubstituted phenyl moieties (IC₅₀ = 8.3 ± 2.6 μg/mL) was more effective than cisplatin (IC₅₀ = 13.7 ± 1.2 μg/mL) against C6 glioma cells. Compound 17 also exhibited DNA synthesis inhibitory activity on C6 cells. Furthermore, compound 17 showed low toxicity to NIH/3T3 cells (IC₅₀ = 416.7 ± 28.9 μg/mL).