Hybrid molecules furnished by merging two or more pharmacophores is an emerging concept in the field of medicinal chemistry and drug discovery. Currently, coumarin hybrids have attracted the keen attention of researchers to discover their therapeutic capability against cancer. Objective: The present study aimed to evaluate the in vitro antitumor activity of a new series of hybrid molecules containing coumarin and quinolinone moieties 4 and 5 against four cancer cell lines. Materials and Methods: A new series of hybrid molecules containing coumarin and quinolinone moieties, 4a-c and 5a-c, were synthesized and screened for their cytotoxicity against prostate PC-3, breast MCF-7, colon HCT- 116 and liver HepG2 cancer cell lines as well as normal breast Hs-371 T. Results: All the synthesized compounds were assessed for their in vitro antiproliferative activity against four cancer cell lines and severa