Decidualization is an essential process of endometrial differentiation for embryo implantation and maintenance of pregnancy. Recently, uterine movement-induced mechanical stress is noticed to have possible effects on endometrial functions. In this study, we addressed the possible effect of mechanical stress on the process of decidualization of endometrial stromal cells (ESC). Endometrial stromal cells (ESC) were cultured on flexible-bottomed culture plates. After achieving decidualization with estradiol and progesterone for 12 days, cultures were continued for 24 h with or without cyclic stretch (25% elongation) in serum-free conditions at a rate of two cycles per minute using a computer-operated cell tension system. Concentrations of insulin-like growth factor binding protein-1 (IGFBP-1), a marker of decidualization, in the conditioned medium were measured using a specific ELISA, and IGFBP-1 mRNA expression in the ESC was measured by RT-PCR. Cyclic stretch remarkably increased IGFBP-1 secretion from decidualized ESC. It also increased IGFBP-1 mRNA in decidualized ESC. The increase in IGFBP-1 secretion was inhibited by actinomycin D, but not by indomethacin, PD98059, or H89. The conditioned medium of decidualized ESC cultured with cyclic stretch increased IGFBP-1 secretion from decidualized ESC cultured under stationary conditions. These findings imply that uterine movement modulates decidualization of the endometrium and has a regulatory effect on reproduction.