Objective Benzoquinone ansamycin antibiotic, geldanamycin (GA), is a new anticancer agent that could inhibit Hsp90 by occupying its NH2-terminal ATP-binding site. This study was to investigate the antitumor efficacy of GA on Her2/neu tyrosine kinase overexpressing human breast cancer cell line SKBr3. Methods The degradation of Her2/neu tyrosine kinase was analyzed by Western blotting, the proliferation index was determined by MTT assay,cell cycle distribution was detected by flow cytometry, Cyclin D1 mRNA transcription was measured by RT-PCR and real-time PCR, and cell motility was evaluated by the cell culture insert model. Results GA induced a dose- and a time-dependent degradation of the Her2/neu tyrosine kinase protein and concurrently, the inhibition of cancer cell proliferation. The antitumor effects mediated by GA included: GA treatment decreased the survival rates of cancer cells,and led to a dase-dependent G1 arrest. Furthermore, this antitumor effect was proved to be related to declined transcription of Cyclin D1. Concurrently, the motility of cancer cells was reduced by GA. Conclusion GA treatment could induce the degradation of Her2/neu tyrnsine kinase efficiently, inhibit cancer cell proliferation and reduce motility in Her2/nen tyrosine kinase overexpressed human breast cancer cell line SKBr3.