Abstract: Objective To detect state of HER2 amplification in breast cancer and assess its clinicopathological significance. Methods To analyze HER2 amplification/protein expressing status in 55 cases of breast cancer specimens with fluorescence in situ hybridization(FISH) and immunohistochemistry (IHC)，and the relationship wity clinicopathological characters.To compare the coincidence of the two assay methods(IHC and FISH). Results Thirty-two of the 55 cases (58.2%) of breast cancer showed HER2 amplification.Twenty-one of the 22 cases (95.5%) with HER2(3+) by immunohistochemistry was HER2 amplification by FISH testing.Ten of the 12 cases (83.3%) with HER2(2+) by immunohistochemistry were HER2 amplification by FISH testing.Only one of the 21 cases (4.7%) with HER2(+/－) by immunohistochemistry was HER2 amplification by FISH testing.Thirty of the 39 cases(76.9%) with invasive ductal carcinomas identified HER2 amplification.Only one of the 12 cases(8.3%) with invasive lobular carcinoma identified HER2 amplification.The presence of HER2 amplification was significant difference between histologic grade of the invasive ductal carcinoma(P<0.001).Grades Ⅲ invasive ductal carcinomas were more likely to demonstrate HER2 amplification than grade Ⅰand Ⅱ ductal carcinoma.The presence of HER2 amplification was significantly correlated with negative ER and PR（P<0.01），and not related to postmenopausal（P>0.05）. Conclusion The presence of HER2 amplification was less surprising in invasive lobular carcinoma and positive ER，PR and grade I invasive ductal carcinomas.We suggest that grade Ⅲ invasive ductal carcinomas with negative ER and PR although the results was negative by IHC，detection of the neoplasm should be performed to confirm HER2 amplification by FISH testing.