A series of 5-phenyl-4, 5-dihydro-1, 3, 4-thiadiazoles were synthesized and their cytotoxicity was examined against four human cancer cell lines, eg lung cancer (A549), ovarian cancer (SK-OV-3), skin cancer (SK-MEL-2), and colon cancer (HCT15). The title compounds were synthesized by condensation of thiosemicarbazide with substituted benzaldehydes, followed by cyclization with acetic anhydrides in good yields. Most of the compounds exhibited ...