Purpose of investigation: The authors examined whether isoflavone can effectively increase the secretion of cytokines associated with implantation from endometrial glandular cells. Material and Methods: Endometrial tissue was collected from 14 patients who underwent surgery for benign gynecological diseases in this hospital. The endometrial tissue was separated into stromal and glandular cells, and isoflavone was added to the glandular cells at a concentration of 0, 0.05, 0.5, and 5 μg/ml. In another group, an estrogen receptor antagonist was added together with isoflavone. After 24 hours, the expression levels of leukemia inhibitory factor, interleukin (IL)-6, IL-11, and IL-6 signal transducer glycoprotein 130 (IL-6/gp130) were measured by quantitative polymerase chain reaction. Results: A significant increase in the expression of IL-6/gp130 was found in glandular cells treated with isoflavone (0.5 μg/ml). The significant differences were not observed among the groups upon treatment with isoflavone and an estrogen receptor antagonist, indicating that isoflavone acted via the estrogen receptor. Conclusion: Isoflavone increases the mRNA expression levels of IL-6/gp130 in human endometrial glandular cells of early to mid secretary phase.