We herein report a case of acute kidney injury and Fanconi syndrome associated with a red yeast rice supplement. A 72-year-old woman's serum creatinine rose from 0.7 to 3.97 mg/dL after starting the supplement, accompanied by metabolic acidosis, proteinuria, hematuria, and glucosuria. A kidney biopsy showed proximal tubular injury without abundant tubulitis. Immunostaining showed dilated tubules that were positive for CD10, confirming proximal tubule localization. Discontinuation of the supplement and steroid pulse therapy improved the patient's condition. This case highlights the health risks associated with unregulated dietary supplementation.