Calcium (Ca²⁺) is an important regulator of apoptotic signaling. Calbindin‐D_9k (CaBP‐9k) and ‐D_28k (CaBP‐28k) have a high affinity for Ca²⁺ ions. Uterine calbindins appear to be involved in the regulation of myometrial activity by intracellular Ca²⁺. In addition, uterine calbindins are expressed in the mouse endometrium and are regulated by steroid hormones during implantation and development. The aim of the present study was to evaluate the regulation of apoptosis in the uteri of CaBP‐9k, CaBP‐28k, and CaBP‐9k/28k knockout (KO) mice. Our findings indicated that Bax protein was enhanced in the uteri of CaBP‐28k and CaBP‐9k/28k KO mice compared to wild‐type (WT) and CaBP‐9k KO mice, but no difference was observed in Bcl‐2 protein expression. The expressions of caspase 3, 6, and 7 proteins were higher in both CaBP‐28k and CaBP‐9k/28k KO mice than in WT and CaBP‐9k KO mice. These results suggest that the absence of CaBP‐28k increases apoptotic signaling. We also investigated the expression of endoplasmic reticulum (ER) stress genes by Western blot analysis in calbindin KO mice. C/EBP homologous protein and immunoglobulin heavy chain‐binding protein protein levels were elevated in CaBP‐28k KO mice compared to WT mice. When immature mice were treated with 17β‐estradiol (E2) or progesterone (P4) for 3 days, we found that the expressions of Bax and caspase 3 protein were increased by E2 treatment in WT and CaBP‐9k KO mice, and by P4 treatment in CaBP‐28k KO mice. These results indicate that CaBP‐28k blocks the up‐regulation of apoptosis‐related genes and ER stress genes, implying that CaBP‐28k may decrease the expression of genes involved in apoptosis and ER stress in murine uterine tissue. J. Cell. Biochem. 113: 194–203, 2012. © 2011 Wiley Periodicals, Inc.