Polycystic ovary syndrome (PCOS) frequently exhibits hyperinsulinemia due to insulin resistance, but there are many unknown aspects of this disease. This report presents the case of a 31-year-old woman with PCOS and type B insulin resistance syndrome (TBIRS). The patient had repeated hyperglycemia and hypoglycemia, and prominent hyperinsulinemia. The insulin receptor antibody was positive, leading to a diagnosis of TBIRS. She also had amenorrhea during the previous 3 months, high blood testosterone levels, and enlarged polycystic ovaries, leading to a diagnosis of PCOS at the same time. The patient was treated with glucocorticoid for TBIRS. The insulin receptor antibody eliminated at 8 weeks after initiation of glucocorticoid treatment, and the blood glucose levels and hyperinsulinemia improved at 9 weeks. Then, the enlargement of both ovaries diminished at 32 weeks, and the menstruation had normalized since 36 weeks. The blood testosterone level normalized at 41 weeks. To the best of our knowledge, this is the first report to demonstrate that enlarged polycystic ovaries and a menstrual disorder in TBIRS improved after glucocorticoid treatment. It is possible that elimination of insulin receptor antibodies by glucocorticoid treatment attenuated insulin resistance and subsequently improved PCOS in TBIRS.