To synthesize a new series of carbostyril-3 '-carbonitrilselenophene hybrid compounds, Pechmann coumarin compounds were reacted with 2-amino-3 '-carbonitrilselenophene derivatives and their anticancer activities on MCF7 and DU145 cell lines and antioxidant activities were investigated. Anticancer and antioxidant activities of the starting compounds and their corresponding new hybrid compounds were compared. It was determined that IC(50)values of hybrid compounds (3e,3f,3g, and3h)on the MCF7 breast cancer cell line showed the highest cytotoxic activity with 7.99, 3.64, 7.72, and 2.74 mu M values, respectively. In the case of anticancer activity on the DU145 prostate cancer cell line, compounds3fand3hwere found to have the highest cytotoxic activity with IC(50)values of 4.21 and 3.90 mu M, respectively. The compound3gis also the most radical scavenging compound with an inhibition value of 88.78%.