A 51-year-old woman was admitted to our hospital for acute kidney injury (AKI) with an elevated serum creatinine level of 5.07 mg/dL and Fanconi syndrome. The patient was discharged after partial recovery of kidney dysfunction with conservative treatment but was readmitted approximately three months later due to a recurrence of AKI with Fanconi syndrome. A kidney biopsy revealed findings consistent with acute tubular necrosis and localized tubulointerstitial nephritis, with no specific vascular or glomerular lesions. The patient’s medical history revealed that prior to both AKI episodes, the patient had been taking “Red Yeast Cholestehelp”, a lipid-lowering supplement for a period of time. Her kidney dysfunction and Fanconi syndrome improved with the discontinuation of the supplement and correction with oral medications. In Japan, a series of similar health hazards related to the red yeast rice supplement has been reported, but the causative toxin and its causal relationship with AKI have not been established. The present case provides firm evidence that clinically supports this relationship.