The lower the Ki67 positivity rate of breast cancer, the better, and currently ≤14% is often appropriate. Ki67 is a kind of tumor proliferation-related antigen, which is a reliable indicator of tumor proliferation activity because it does not exist in G0 nuclear quiescence and has a short half-life. Generally speaking, a higher Ki67 positive rate indicates higher tumor proliferation activity, poorer tumor differentiation, higher malignancy, higher risk of recurrence and metastasis, and poorer prognosis. Therefore, the lower the Ki67 positive rate, the better. However, as far as Ki67 is concerned, negative is better than positive, and low expression is better than high expression. However, the degree of malignancy and prognosis of breast cancer are also related to the stage, grading, molecular typing, etc. It is recommended to choose the appropriate treatment plan after consulting with a specialist.