Mannitol, a hyperosmotic agent, is commonly used in hemodialysis for eliminating the symptoms of dialysis disequilibrium syndrome. Mannitol extravasation is a potential complication which will induce fluid shift out of vessel, thrombophlebitis, bullous eruption and even compartment syndrome. We reported a case of mannitol extravasation due to improper mannitol infusion site during first hemodialysis.