Although nobiletin has a potent antitumor activity against several types of human cancers, its inhibitory effects and possible mechanisms of action on breast cancer cells with different hormone receptor and HER2 status remains unknown. Materials and Methods: Using hormone receptor-positive MCF-7, HER2-positive SK-BR-3, and triple-negative MDA-MB-468 cell lines, we investigated the antitumor mechanisms of nobiletin. Results: Nobiletin exhibited dose- and time-dependent antitumor activity against these different subtypes of cell lines, with the greatest inhibition observed against the MDA-MB-468 cell line. Nobiletin induced cell-cycle arrest at the G(0)/G(1) phase by suppressing ERK1/2 activity, with concomitant cyclin-D1 suppression and p21 up-regulation. Nobiletin induced apoptotic cell death by reducing Bcl-xL expression, without affecting Bax levels, and inhibited the activity of AKT and downstream mTOR in MDA-MB-468 cells, but not in other cell lines. Conclusion: The predominant anticancer activity of nobiletin in MDA-MB-468 cells suggests a potential role of nobiletin for the prevention of triple-negative breast cancer.