Purpose: Gleditsiae spina (GS) has been used to treat patients with several diseases such as carbuncle, swelling and parasites. Recently GS is known to have anticancer activity in abdominal solid tumor, but the effects of GS on breast cancers is not clarified. For these reasons, we investigated effects of Gleditsiae spina (GS) on gene expression of human breast cancer cells. Methods: We investigated the effects of GS on proliferation of breast cancer cell line, MDA-MB-231. In addition, the genetic profile for the effect of GS on breast cancer cells was measured using microarray technique, and the functional analysis on these genes was conducted. Results: Total 1,434 genes were up-regulated and 2,483 genes down-regulated in the cells treated with GS. Genes induced or suppressed by GS were all mainly concerned with metabolic process, regulation of biological process and protein binding. The network of total protein interactions was measured using cytoscape program, and some key molecules that can be used for elucidation of therapeutical mechanism of medicine in future were identified. Conclusion: These results suggest possibility of GS as anti-cancer drug for breast cancer, and also suggest that related mechanisms are involved in regulation of intra-cellular metabolism in breast cancer cells.