Abstract: An air vent stopper is provided for a ventilation grill having a plurality of ribs mounted within an opening in a building wall. The air vent stopper consists of a plate being of a size and shape to completely cover over the ribs in the ventilation grill. A gasket being of a same size and shape as the plate is positioned between the plate and the ventilation grill. Clip-on U-shaped clamp is for removably securing the plate with the gasket to some of the ribs of the ventilation grill, so as to completely seal the ventilation grill from leaking air therethrough during cold weather conditions.