Background <p>Triple-negative breast cancer (TNBC) is one of the most malignant subtypes of breast cancer with a high recurrence rate and adverse prognosis. Due to the lack of reliable molecular targets, improving patients’ outcomes is still a challenge in the clinic. The clinical significance of miR-4326 and its potential in mediating tumor progression were investigated in this study, aiming to explore a novel biomarker for TNBC.</p> Methods <p>A total of 108 patients diagnosed with TNBC were included in the present study, and the tissue samples were collected. The expression of miR-4326 was evaluated using PCR, while its clinical significance was assessed from the perspectives of disease severity and 5-year prognosis. In vitro, the regulation of TNBC cell growth and motility by miR-4326 was evaluated by CCK8 and Transwell assays with the help of cell transfection.</p> Results <p>Upregulation of miR-4326 was observed in tumor tissues of TNBC patients, which indicates advanced TNM stage, the occurrence of lymph node metastasis, and poorer prognosis. In TNBC cells, miR-4326 was also upregulated, its knockdown significantly suppressed cell proliferation, migration, and invasion. MED13 showed opposite dysregulation and was negatively regulated by miR-4326. Silencing MED13 could reverse the suppressive effect of miR-4326 knockdown on TNBC cells.</p> Conclusions <p>miR-4326 could serve as a prognostic biomarker for TNBC and regulate tumor progression via targeting MED13.</p>