The cytosolic phosphoprotein stathmin is upregulated at the site of embryo implantation in the rodents. However, stathmin expression in the human uterus has not yet been investigated. The distribution of uterine and placental stathmin was analyzed by immunohistochemistry, while stathmin mRNA expression was detected in endometrial tissues by the reverse transcriptase-PCR. Cultured endometrial stromal cells were used to investigate whether stathmin plays a role in decidualization. Stathmin is expressed specifically in the glandular epithelium and the stromal cells of human endometrial tissue. It is also expressed by cytotrophoblasts and extravillous trophoblasts, but not by syncytiotrophoblasts or decidual tissues during the first trimester of pregnancy. When stromal cells isolated from normal endometrial tissues were cultured and stimulated to decidualize by progesterone (P4) plus estrogen or dibutyryl cyclic 3',5'-AMP, their total and phosphorylated stathmin levels decreased. Knocking down stathmin expression in the cultured stromal cells using small interfering RNA, before the cells were exposed to the decidualizing agents, significantly suppressed decidualization, as indicated by the decreased expression of IGF-binding protein-1 and prolactin. Stathmin is differently expressed in human endometrial and placental cells and may participate in the decidualization of endometrial stromal cells.