Objective：To explore the expression of MMP3 and extracellular matrix metalloproteinase inducer (EMMPRIN) in benign and malignant breast lesions and its relevance. Methods: Using immunohistochemical method, we examined the expression of MMP3 and EMMPRIN proteins in 58 breast cancer specimens，28 premalignant lesions, 40 hyperplasia specimens, 40 benign tumor specimens and 20 normal breast tissues. The expression of MMP3 mRNA and EMMPRIN mRNA was examined using in situ hybridization in 20 breast cancer specimens，20 premalignant lesions, 20 hyperplasia specimens, 20 benign tumor specimens and 20 normal breast tissues. The values of integral optic density （IOD）of the expression was calculated by image analysis system. Results: The expression of MMP3 and EMMPRIN proteins and mRNA was stronger in breast cancer and premalignant lesions than in the other lesions. The IODs of MMP3 and EMMPRIN proteins and mRNA in breast cancer and premalignant lesion were significantly higher than those of hyperplasia, benign tumors and normal breast tissues（P＜0.01）; there was no significant differences between the first 2 groups and between the last 3 groups. Expression of EMMPRIN in breast cancer patients with lymphatic metastasis was higher than those without lymphatic metastasis (P<0.05). MMP3 mRNA expression was positively correlated with EMMPRIN mRNA expression in all groups, but the correlation between expression of MMP3 and EMMPRIN proteins was different in different groups. Conclusion: Overexpression of MMP3 and EMMPRIN may play an important role in the malignant transformation of breast lesions. Patients with high expression of EMMPRIN are more likely to have lymphatic metastasis.