The present invention relates to a hair cutter for a drain which can finely cut hair caught in a filter of the drain in a bathtub to discharge the hair together with water through the drain, and can be used as a water stopper sealing the drain. The hair cutter of a drain comprises a filter installed on the drain to discharge water, comprising multiple catching ribs with cutting holes formed thereon, a pressing plate pressing hair caught by the catching ribs of the filter; a cutting assembly composed of multiple blades penetrating the cutting holes to cut the hair pressed by the pressing plate; multiple position guiding convex units along the edge of the upper part of the filter at constant distance apart to guide a position where the blades of the cutting assembly pass through the cutting holes; and multiple position guiding concave units provided on the cutting assembly to form concavo-convex connection with the position guiding convex unit.
