Breast cancer is one of the most common types of carcinoma in humans. The aim of the present study was to identify the role of Notch 1 in the proliferation and invasion of human breast cancer cells. Firstly, the levels of Notch 1 were determined by western blot analysis in breast cancer cell lines, and the results revealed that the expression levels of Notch 1 were markedly higher in MDA‑MB‑231 and MCF‑7 cells, and lower in MCF‑10A cells, compared with human mammary epithelial cells. An MTT assay was used to determine the viability of breast cancer cells. The optical density (OD)490 values were significantly decreased in Notch 1 short hairpin (sh)RNA‑transfected MCF‑7 and MDA‑MB‑231 cells, compared with the OD490 values in the negative control shRNA‑transfected cells. The MCF‑7 cells and MDA‑MB‑231 cells were also treated with increasing concentrations of MRK003, a Notch 1 inhibitor, for 24, 48 and 72 h, respectively. The inhibition rate was gradually increased in the MRK003‑treated cells in a time‑ and dose‑dependent manner. The invasive ability of the cells was determined using a Transwell migration assay. The migration ability was significantly decreased in the Notch 1‑transfected MCF‑7 cells and MDA‑MB‑231 cells. The molecular mechanism was examined, and the knockdown of Notch 1 significantly decreased the expression levels of β‑catenin, matrix metalloproteinase (MMP)‑2 and MMP‑9, and was also correlated with the downregulation of β‑catenin in the nucleus. In conclusion, Notch 1 was key in the progression of breast cancer, and knocking down the expression of Notch 1 significantly suppressed the proliferation and invasion of breast cancer cells. This provides novel clues for cancer therapy in human breast cancer.