Background: Breast cancer (BC) is the most common cancer for women and its incidence is gradually increasing. Here, the serum levels of basal cytokeratin 17 (CK17) and its association with clinicopathological characteristics of patients with invasive ductal breast carcinomas(IDBC) were investigated. Methods: Preoperative/pretreatment sera were obtained from 78 female patients with IDBC and sera from 24 age-matched healthy females were used as controls. Serum levels of CK17 were determined using sandwich ELISA. Statistical analysis was performed using SPSS program. Results: Serum CK17 levels were significantly higher in IDBC patients (1.26± 0.11; 0.93ng/mL) than controls(0.24± 0.01;0.23ng/mL). Statistical analysis showed that CK17 serum levels significantly correlated with age, menopausal status, tumor size, histologic grad, and pTNM stage of IDBC patients. Moreover, higher mean CK17 levels significantly associated with triple-negative subtype. At the best cut-off level (0.31), the CK17 assay showed area under ROC curve of 0.944 indicating high diagnostic performances. Conclusion: The serum CK17 may be a prerequisite marker in invasive ductal breast carcinoma.