Ostruthin, isolated from Paramignya trimera, was used as a scaffold to design its alkyl triphenylphosphonium derivatives. With the optimal reaction conditions in hand, five alkyl triphenylphosphonium ostruthin derivatives (1–5) were synthesized. Ostruthin and its derivatives were tested for cytotoxicity against human PANC‐1 pancreatic, Hela cervical, and HepG2 liver cancer cell lines. Ostruthin and its hexyl and heptyl triphenylphosphonium derivatives (4 and 5) showed strong preferential cytotoxicity against PANC‐1 cells with the PC50 values of 10.3 and 14.4 μM, respectively. In addition, compounds 4 and 5 also exhibited potent cytotoxicity towards HeLa cells with the IC50 values of 24.8 and 18.5 μM, respectively. The hexyl triphenylphosphonium group in 4 was found to slightly enhance cytotoxicity against HepG2 cells. Further, the morphological changes and the live‐cell imaging result suggested the anticancer potential against HeLa cells of the synthesized ostruthin derivative 5.