A 56-year-old woman with diabetes mellitus experienced a reduction in blood glucose levels after consuming boiled mangosteen's skin water for 2 weeks. The patient's blood glucose levels decreased from 223 mg/dL to 206 mg/dL. This case report is supported by previous research on the antihyperglycemic effects of xanthones γ-mangosteen, a compound found in mangosteen's skin. The study suggests that mangosteen's skin may be a potential natural remedy for reducing blood sugar levels in patients with diabetes mellitus, and further research is warranted to explore its therapeutic potential.