Objective: To investigate the expression of protein arginine methyltransferase 1 (PRMT1) in breast cancer and to evaluate its clinical significance. Methods: Bioinformatics databases, including TIMER3.0, GEPIA2, and UALCAN, were utilized to analyze PRMT1 mRNA expression levels in breast cancer tissues. Tissue microarray and immunohistochemistry were employed to detect PRMT1 protein expression in breast cancer tissues and to explore its correlation with clinicopathological features. Survival analysis based on Gene Expression Omnibus (GEO) datasets using the OSdream online tool was performed to assess the association between PRMT1 expression levels and recurrence-free survival (RFS) and metastasis-free survival (MFS) in breast cancer patients. The diagnostic value of PRMT1 for breast cancer was evaluated by receiver operating characteristic (ROC) curve analysis. Results: Multi-database bioinformatics analysis revealed that, compared to normal tissues, PRMT1 mRNA expression was significantly elevated in breast cancer tissues (P < 0.01). Elevated PRMT1 mRNA levels were closely associated with advanced clinical stage and lymph node metastasis (P < 0.01). Immunohistochemical staining of tissue microarrays confirmed that PRMT1 protein expression was significantly higher in breast cancer tissues compared to adjacent normal tissues (P < 0.01). High PRMT1 expression was positively correlated with advanced clinical stage and lymph node metastasis in breast cancer patients(P < 0.01). Survival analysis indicated that breast cancer patients with high PRMT1 expression had a significantly shorter RFS and MFS compared to those with low PRMT1 expression (P < 0.05). The receiver operating characteristic (ROC) curve analysis showed that the area under the curve (AUC) was 0.927(95%CI: 0.887-0.967, P < 0.001). At the optimal cutoff value of 1.167, the sensitivity and specificity were 82.5% and 90.0%, respectively, indicating robust diagnostic performance of PRMT1 for breast cancer. Conclusion: PRMT1 is highly expressed in breast cancer tissues, and elevated PRMT1 expression is associated with advanced clinical stage, lymph node metastasis, and poor prognosis in breast cancer patients. PRMT1 demonstrates excellent diagnostic efficacy for breast cancer. Therefore, PRMT1 may serve as a potential biomarker for the diagnosis and prognostic evaluation of breast cancer.