Background and Aims: YKL-40 is an extracelluar matrix glycoprotein with sequence homology to the proteins of the chitinase like family, but has no chitinase activity. It is highly expressed in several types of cancer, including breast cancer. In this study we aim to detect YKL-40 expression and its polymorphism in metastatic and non-metastatic breast cancer patients and comparing the results with fibroadenoma patients and normal females.Patients and Methods: The study included 113 female patients, dividedinto 20 patients with fibroadenoma , 73 non-metastatic & 20 metastatic breast cancer patients. Twenty healthy females were also included and served as control. YKL-40 level was detected in serum of studied groups using ELISA kit, also DNA extraction was done followed by real time PCR to detect the chitinase 3-like I (rs4950928) polymorphism. Results: There was statistical significant difference regarding YKL-40 level between the control group versus non-metastatic group as well as metastatic group, and between fibroadenoma group and non-metastatic as well as metastatic breast cancer group (P<.001 each). Also there is statistical significant difference between breast cancer and control groups regarding genotype GC (P = 0.04) and between fibroadenoma and breast cancer groups also regarding genotype GC (P = 0.042). Conclusion: YKL-40 expression and its polymorphism may be useful as a potential biomarker in breast carcinoma.