Objective：To apply chromogenic in situ hybridization (CISH) for detection of HER2 gene amplification in breast cancer tissues and to discuss some modifications of the CISH method. Methods: HER2 gene amplification was detected by CISH in 60 breast cancer specimens with an immunohistochemical score over 2+. The correlation between the results of IHC and CISH was analyzed.Our experience in CISH manipulation was summarized and optimization to CISH was discussed. Results: CISH identified gene amplification in 91％(40/44) specimens with an IHC score of 3+ and in 50％(8/16) specimens with an IHC score of 2+．The total concordance rate between IHC and CISH was 80％(48/60, P<0.01)．The thickness of sections should be controlled within 4-5 μm; the denaturation should be complete; and the post-hybridization washing temperature and time were also very important and the temperature should be controlled at 70-75℃. The dyeing time of hematoxylin should also be restrictedly controlled. Positive control should be set up in the experiment for high quality of the experiment. Conclusion: CISH has high concordance rate with IHC in examining HER2 amplification and it may be a new method for detection of HER2 gene. The thickness of the sections, the post-hybridization washing temperature and time, and the time of hematoxylin dyeing should be strictly controlled.