A ultraviolet bacteria-killing system for water closet cover is described, comprising: a supporting base (1) a UV lamp (2) placed on the base (1) a transparent cover (3) adapted to cover the UV lamp (2) and connected to the base (1) supply means (10) of the UV lamp (2) operatively and externally connected to the UV lamp (2) and level sensor means (6) adapted to control the switching-off of the UV lamp (2) when the water closet cover is lifted to use the water closet.
