We tested the anticarcinogenic effect of alpha-linolenic acid (ALA) as a single compound. To test the role of ALA in breast cancer cells (MCF-7), we analyzed the antiproliferative pathway and the proapoptotic pathway. ALA exhibited growth inhibition on MCF-7 cells dose-dependently of ALA in 24, 48, and 72 h, without possible cytotoxicity per se. ALA enhanced the cell growth-inhibitory activity in a dose-dependent manner. Second, the proapoptotic pathway showed a sub-G(1) accumulation with concomitant upregulation of proapoptotic Bax expression, as well as a downregulation of antiapoptotic Bcl-2 expression dose-dependently, causing the Bcl-2/Bax ratio to decrease by about 50%. Subsequent cytochrome c release and proteolytic activation of caspase-3 followed by proteolytic cleavage of poly(ADP-ribose) polymerase all suggest ensuing progression to apoptosis. This finding suggests that ALA alone might also be responsible for growth-inhibitory and proapoptotic effects on estrogen-positive breast cancer cells.