In situ hybridization data showed an increase in XBP1 (S) and HSPA5 mRNA expression in granulosa cells of PCOS mice and immunohistochemical analysis revealed an increase in the immunoreactivity of CHOP, phospho-IRE1, and phospho-PERK in granulosa cells of PCOS mice, consistent with the findings in human granulosa cells of PCOS patients. Here, XBP1 is linked to polycystic ovary syndrome.