We report a patient with mixed connective tissue disease who developed accelerated hypertension, acute renal insufficiency, and microangiopathic hemolytic anemia. A renal biopsy specimen showed marked vascular changes in small arteries consisting of laminated endothelial cell proliferation and luminal thrombosis, which were similar to those of scleroderma renal crisis. This patient was successfully treated with an angiotensin-converting enzyme inhibitor as well as analogues of prostaglandin E1 and prostaglandin I2. In patients with mixed connective tissue disease, a fatal complication like scleroderma renal crisis should be considered when the blood pressure rapidly increases. The combined administration of angiotensin-converting enzyme inhibitors and analogues of prostaglandin E1 and prostaglandin I2 may be an effective treatment for this complication.