The destruction of cancer cells with chemotherapeutic agents is normally achieved through apoptosis. We previously introduced two synthetic halogenated flavanone derivatives, 3^′,7-dichloroflavanone (3′-7 DCF) and 3^′,6-dichloroflavanone (3′-6 DCF), as potential apoptosis-inducing agents. In the current study, we investigated the ability of these compounds in triggering intrinsic or/and extrinsic pathway of apoptosis in breast and prostate cancer cells. Also, the synergistic effect of 3′-7 DCF with TLR3 (Toll-like receptor 3) agonist in apoptosis induction was evaluated on PC3 and LNCaP human prostate cancer cells. The involved pathway of apoptosis in the treated cells was delineated by caspase-3 activity assay, PARP-1 (poly(ADP-ribose)polymerase-1) cleavage, and procaspase-9 cleavage as markers of the intrinsic pathway and procaspase-8 cleavage as the marker of the extrinsic pathway. With the exception of the normal cells, treatment of all cell lines with both 3′-7 DCF and 3′-6 DCF triggered the cleavage of procaspase-8 and procaspase-9. These results indicate that the intrinsic and the extrinsic pathways of apoptosis are the mechanisms of the toxicity of flavanones in these cancer cell lines. However, the cytoxicity of the compound 3′-7 DCF was not synergistic with TLR3 agonist. Interestingly, the activation of caspases-9 preceeded that of caspase-8 suggesting that the intrinsic pathway is the primary reason for apoptosis induction by the flavanones.