To explore the cyclic changes of S100A10 expression in human endometrium.The gene and protein expression of S100A10 in human endometrium was examined by real-time polymerase chain reaction (PCR), immunohistochemical staining and Western blot.S100A10 protein was predominantly expressed in cytoplasm and cytomembrane of luminal and glandular epithelia. The S100A10 protein was continuously expressed from proliferative phase to secretory phase of menstrual cycle. However the expression in the secretory phase was much higher than in the proliferative phase (2.26 ± 0.17, 3.75 ± 0.22, 2.65 ± 0.20 vs 1.17 ± 0.11, 1.32 ± 0.14, both P < 0.05). Specifically, the highest level of S100A10 expression occurred during the mid-secretory phase. Then real-time PCR was used to analyze the mRNA expression of S100A10 in human endometrial samples at various points during the menstrual cycle. And the results confirmed the corresponding changes at the genetic level (0.50 ± 0.05, 1.02 ± 0.10, 0.55 ± 0.05 vs 0.25 ± 0.02, 0.30 ± 0.03, both P < 0.05).The endometrial expression of S100A10 increases during the window of embryo implantation. It suggests that it may increase the endometrial receptivity of uterine epithelial cells for embryos.