The Y-box binding protein 1 (YB-1) is a multifunctional cold shock domain protein which has physiological roles in growth and development, transcription, DNA repair and translation. However, YB-1 is also widely reported to be involved in tumorigenesis with roles in tumor growth, metastasis and chemoresistance. The aim of this study is to determine the association of the expression of YB-1 in invasive ductal carcinoma tissue samples with clinicopathological parameters of breast cancer patients. Immunohistochemical staining of the YB-1 protein was performed on breast cancer tissue microarrays. The intensity of YB-1 staining and its percentage were scored and immunoreactivity score (IRS) was computed. Chi-square or Fisher’s Exact Test was used to determine the association of IRS of YB-1 with parameters such as age, tumor size, mitotic index, lymph node metastasis and estrogen receptor status. The specificity of the antibody was verified by Western Blotting. Cytoplasmic staining of the breast cancer cells was observed and a higher expression of YB-1 was significantly associated with higher grade of tumor, increased mitotic index and estrogen receptor negative status. There was also an association between the expression of YB-1 and tumor size with borderline significance. Since mitotic index and tumor size are proliferation parameters, the correlation of YB-1 with a proliferation marker, proliferating cell nuclear antigen (PCNA) was evaluated. There was a significant correlation between YB-1 and PCNA. Multivariate analysis revealed that a higher expression of YB-1 increased the risk of having higher mitotic index by 4.5 times. The results showed that YB-1 is a potential biomarker for breast cancer and further studies done on this protein could give rise to a promising target for the prognosis and treatment of breast cancer.