Heterocyclic rings are recognized as key components of many natural, semi-synthetic and synthetic molecules with a broad spectrum of biological activities. Among these molecules, the indole and imidazo[2,1-b][1,3,4]thiadiazole systems have recently been described as useful scaffolds for the design of anticancer agents. Herein the antitumor activity of a series of 3-(6-phenylimidazo[2,1-b][1,3,4]thiadiazol-2-yl)-1H-indoles, designed as hybrid structures, was assessed. Seven out of 10 compounds (1a-g) were submitted to National Cancer Institute (NCI). Remarkably, compound 1g showed antiproliferative activity against the full panel of sixty human cancer lines, with half-maximal inhibitory concentration of between 1.67 and 10.3 μM. Further studies showed antiproliferative activity of 1a-g and of three additional compounds 1h, 1i and 1l, with different substituents on the indole nucleus and phenyl ring, against three pancreatic cancer cell lines. In particular, derivatives 1g and 1h inhibited both proliferation and migration of SUIT-2 cells at concentrations lower than 10 μM. In conclusion, new indole derivatives are characterized by in vitro antitumor activity, supporting future mechanistic studies.