Background: Matrix metalloproteinase-9 (MMP-9), an enzyme with major role in remodeling of extracellular matrix, has been the focus of attention in some previous studies in the field of breast cancer. In the current study the relationship between matrix metalloproteinase-9 and some clinicopathological factors of breast carcinoma has also been evaluated. Methods: Formalin-fixed and paraffin-embedded tissue specimens from three groups including 40 invasive breast carcinoma (tumor group) and their adjacent normal tissue (tumor control), as well as 40 normal mammoplasty specimens (normal control) were studied. The samples were from the pathology archive of Alzahra Hospital, Isfahan, Iran, from 2016 to 2018. The status of intraepithelial MMP-9 were studied and compared in these three groups using immunohistochemistry. Results: The extent of intraepithelial MMP-9 immunostaining in all positive specimens was 100%. The results of intraepithelial MMP-9 staining intensity was as follow: 12.5% strong, 27.5% moderate, 27.5% mild, and 32.5% negative in tumor group; 17.5% strong, 22.5% moderate, 32.5% mild, and 27.5% negative in tumor control group; and 10% strong, 40% moderate, 27.5% mild, and 22.5% negative in normal control group. Intraepithelial MMP-9 immunostaining intensity showed significant difference between tumor and tumor control groups (P<0.001). Intraepithelial MMP-9 immunostaining intensity showed no significant difference between tumor and normal control groups, and between tumor control and normal control groups (P>0.05). No sig nificant relationship was seen between intraepithelial MMP-9 immunostaining intensity and age, tumor size, tumor grade, and lymph node status in tumor group (P>0.05). Conclusion: Intraepithelial MMP-9 expression increases in some breast carcinomas. Normal breast tissue adjacent to carcinoma does not show such increase. However, intraepithelial MMP-9 expression in breast carcinoma does not show any significant relationship with age, tumor size, tumor grade, and lymph node status.