Background: Expression of kallikrein-11 (KLK11) has been found to be related to the prognosis of various human cancer types but its physiological functions in the steps of breast cancer (BC) progression are still unknown. Materials and Methods: BC and adjacent normal breast tissue samples were collected from 28 patients. KLK11 expression levels were determined by real-time polymerase chain reaction for each sample and associations with known prognostic features were statistically analyzed. Results: Although there was slight up-regulation in tumor tissues overall, significant down-regulation of KLK11 expression in tumor tissue was observed in the elderly and in patients with perineural invasion. Furthermore, tumor size, grade, mitotic score, necrosis, calcification, lymphatic invasion, hormone receptor status and Ki67 expression were associated with altered KLK11 level. Conclusion: Changes in expression levels of KLK11, associated with patient characteristics, might be used as complementary data in order to predict clinical outcome and prognosis in BC.