A series of 2-arylamino-5-(indolyl)-1,3,4-thiadiazoles 6a-v were prepared and studied for their anticancer activity against selected human cancer cell lines. The reaction of indolylhydrazides 3a-h with a variety of aryl isothiocyanates 4 afforded the key intermediate thiosemicarbazides 5a-v, which upon treatment with acetyl chloride produced the 2-arylamino-5-(indolyl)-1,3,4-thiadiazoles 6a-v in good yields. Most of the synthesized compounds showed selective cytotoxicity towards human breast cancer cell line (MDA-MB-231). Of the synthesized 2-arylamino-5-(indolyl)-1,3,4-thiadiazoles, compound 6f is the most potent towards tested cancer cell lines (IC(50) = 0.15-1.18 μM).