Abstract: Objective?To explore the related factors on CD44+CD24-/LowESA+Lin- cell (breast caner stem cell) ratio in breast cancer patients. Methods?Flow cytometry was used to analyze CD44+CD24-/LowESA+Lin- cell ratio in fresh tumor tissues of 40 breast cancer patients administered between March of 2011 and January of 2012 in West China Hospital, Sichuan University, China. Nine individual variables, such as age, clinical stage, histological grade, axillary lymph nodes metastases, immunohistochemisty (IHC) of estrogen receptor (ER), progesterone receptor (PR), C-erbB-2, and Ki-67 were selected to study their correlation with CD44+CD24-/LowESA+Lin- cell ratio. Results?CD44+CD24-/LowESA+Lin- cells were expressed in all breast cancer tissues (median ratio: 4.38%, ranging from 0.5% to 16.8%), in which 20 patients (50.0%) showed low expression less than or equal to 4.38%, whereas, 20 patients (50.0%) demonstrated high expression greater than 4.38%. By univariant analysis, no statistical correlation was observed between CD44+CD24-/LowESA+Lin- cell ratio and the factors like age, tumor size, clinical stage, histological stage, axillary nodes metastasis metastasic, ER, PR. However, when Ki-67 was divided into high expression group (＞32.0%) and low expression group (≤32.0%), statistical difference in CD44+CD24-/LowESA+Lin- cell ratio between the two groups was observed (P=0.008). By multivariate logistic analysis, only Ki-67 expression was the independent factor of breast cancer stem cell expression (P=0.012, OR=6.926, (95%CI,1.529-31.377). Conclusion?In fresh breast cancer tissues, Ki-67 expression was the independent impact factor on CD44+CD24-/LowESA+Lin- cell ratio. Further investigation should be made to explore the correlation of breast cancer stem cell ratio with therapeutic effect and prognosis.