Abstract: ObjectiveTo investigate the expression of inhibitor of differentiation/DNA binding 1(Id1) in breast cancer tissue and its relation to clinicopathological and other molecular parameters. Methods The mRNA expression of Id1 in tissue and MCF -7 cell line of breast cancer were detected by fqRT-PCR.The protein expression of Id1, VEGF in 48 cases of breast carcinoma and 20 cases of breast fibroadenoma tissues of breast were detected by SABC immunohistochemistry. ResultsBy Real-time RT-PCR method，the 2-ΔCT values of the breast carcinoma tissue and breast fibroadenoma tissue were (3.4581±1.3644) and (1.1042±0.0125) respectively.The positive rates of Id1 were significantly higher in breast carcinoma than those in breast fibroadenoma tissues, there were significant difference between the two groups(P<0.05). Spearman rank correlation analysis revealed that the protein expression of Id1 was positively correlated with that of VEGF(r=0.303, P=0.037). No statistical correlation existed among the patients as grouped by age, lymph nodes metastasis, tumor size, histological grading, pTNM stages(P>0.05). ConclusionOver-expression of Id1 exists in the patients with breast cancer.The expression of Id1 is positively correlated with that of VEGF which may be related to blood vessel formation.