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Background Breast cancer (BCa) affects women's health worldwide. BCa subtype could be classified by presenting of oestrogen receptor, progesterone receptor and human epidermal growth factor receptor 2. Knowing of BCa subtype would be benefit for chemotherapeutic treatments guidance. Triple negative breast cancer (TNBC) is a subtype of BCa that lacks of all those receptors and being poor response by currently targeted chemotherapies. The anti-cancer activities of 7-α-hydroxyfrullanolide (GM2) derived from plant Grangea maderaspatana contained potent cytotoxicity against various types of cancer cell lines. However, its mechanism against the TNBC has never been elucidated. Methods We firstly screened the cytotoxic activity of GM2 on non-TNBC (MCF-7); TNBC (MDA-MB-468, MDA-MB-231 and Hs578T); normal breast cell (MCF-12A) and normal fibroblast cell (L-929) by MTT assay. The GM2-treated MDA-MB-468 cells were further investigated for DNA distribution in cell cycle and apoptosis by flow cytometer. Furthermore, proteomic techniques (GeLC-MS/MS) were used to identify altered expression of specific proteins between GM2-treated and untreated MDA-MB-468 cells. Results GM2 had high cytotoxicity effect against breast cancer cell lines (especially TNBC, MDA-MB-468 cell line) and low effect on normal cells. GM2 obviously induced cell cycle arrested at G2/M phase and cell death via apoptosis. Spindle assemble checkpoint protein BUB3 was significantly up-regulated by proteomic analysis after GM2 treatment in MDA-MB-468. p53-independent and p21 pathway might be associated with cell cycle checkpoint. Cell death proteins (Bax, cleaved caspase-7, 8 and 9) and anti-cell death protein (Bcl-2) distinctly increased and decreased respectively in treated MDA-MB-468 cells. These results suggested that those proteins might be the key molecules in triggering mechanism of apoptosis. Conclusions Indeed, GM2 possessed anti-breast cancer property, G2/M arrest and apoptotic induction. This basic knowledge may hopefully lead to further development of targeted therapeutic drug in TNBC patients. Legal entity responsible for the study Department of Biomedical Sciences, Faculty of Medicine, Prince of Songkla University. Funding The Royal Golden Jubilee (RGJ) Ph.D. Programme, The Thailand Research Fund (TRF). Disclosure All authors have declared no conflicts of interest. [ABSTRACT FROM AUTHOR]