Breast cancer (BRCA) is a serious life-threatening cancer, especially triple-negative breast cancer (TNBC). Alcohol dehydrogenase-1B (ADH1B) has recently been revealed to be associated with poor prognosis of BRCA patients. This study identified the exact function of ADH1B on the progression of BRCA and TNBC. ADH1B effect on the prognosis of BRCA and TNBC patients was researched based on online databases and clinical samples. The function of ADH1B on the proliferation, invasion and migration, and growth of BRCA and TNBC cells was investigated by cell counting kit-8, Transwell, and in vivo assays. Western blot was utilized to determine the effect of ADH1B on the mitogen-activated protein kinase (MAPK) signalling pathway activity. As a result, ADH1B was down-regulated in BRCA and TNBC patients and cells, predicting unfavorable prognosis (P<0.05). ADH1B overexpression suppressed the proliferation, invasion and migration, and inactivated the MAPK signalling pathway in BRCA and TNBC cells (P<0.01). ADH1B synergized with Selumetinib (inhibitor of the MAPK signalling pathway) to attenuate the proliferation, invasion and migration of BRCA and TNBC cells (P<0.001). Conversely, Vacquinol-1 (activator of the MAPK signalling pathway) abolished the suppression of ADH1B on the proliferation, invasion and migration of BRCA and TNBC cells (P<0.05). ADH1B suppressed in vivo growth of TNBC cells (P<0.001). Thus, ADH1B may inhibit the proliferation, invasion and migration of BRCA and TNBC cells by inactivating the MAPK signalling pathway. It may be a promising target for the clinical treatment of BRCA and TNBC.