Abstract: An air replenishing fume hood includes a cabinet, a door set, an air replenishing unit and an air guiding unit. The cabinet has an inner casing defining an operating chamber and having an air inlet and an air outlet. A side of the cabinet includes an operation window. A first air passage is formed between the inner casing and the cabinet. The door set includes an outer door leaf adapted to open or close the operation window, and an inner door leaf adapted to open or close the air inlet. An end of the air replenishing unit extends into an external space via an outdoor tube, and another end of the air replenishing unit is connected to the first air passage via an extension tube. The air guiding unit includes an end connected to the air outlet, and another end extending into the external space or a collection tank.