Abstract: Objective 　To explore the possibility of application with the method to detect amplification of HER-2 gene by fluorescence in situhybridization ( FISH) in clinical pathology and molecular targeting therapy in breast cancer, and investigate the relationship between HER-2 gene amplification and clinicopathological data. Methods 　Detecting 50 cases of formalin-fixed and paraffin-embeded breast ductal carcinoma samples compared with result of immunohistochemistry and then analyzed with clinicopathological data. Results 　Sixteen of fifty (32. 0 %) cases of breast carcinoma presented positive for HER-2 protein expression, including 5 strong, 9 moderate and 2 weak expressions, respectively. Eleven of fifty (22. 0 %) cases of breast cancer showed positive for HER-2 gene amplification, in which 5/ 5 was the cases showing st rongly positive and 6/ 9 presenting moderately positive expression for HER-2 protein by immunohistochemist ry. And the one with both amplification of HER-2 gene and polysomy of chromosome 17 was also moderately positive expression for the protein. Both gene amplification and protein expression of HER-2 were corresponding to metastasis of lymph nodes ( P < 0. 05) . Conclusion 　FISH technique can stably detect the amplification of HER-2 gene especially for the positive cases for HER-2 protein and it is clinically useful to select the cases for molecular targeting therapy of Herceptin in breast cancer.