Histone deacetylase 6 (HDAC6) inhibition, recently, has been shown to promote the acetylation of heat-shock protein 90 (Hsp90) and disrupt its chaperone function. Her-2 oncoprotein is identified as a client protein of Hsp90. Therefore, in this study we examined the effect of carbamazepine, which could inhibit HDAC on Hsp90 acetylation and Her-2 stability. The results of this study demonstrate that while carbamazepine had no effect on the Her-2 mRNA level, it induced Her-2 protein degradation via the proteasome pathway by disrupting the chaperone function of Hsp90 in SK-BR-3 cells. Mechanistically, carbamazepine could enhance the acetylation of α-tubulin, indicating its inhibitory effect on HDAC6. Functionally, carbamazepine could synergize with trastuzumab or geldanamycin to promote Her-2 degradation and inhibit breast cancer cell proliferation. Thus, this study has potential clinical implications by providing a promising strategy to overcome the development of resistance against trastuzumab therapy for breast cancer.