A bacteria-killing device for water closet (8) is described, adapted to remove viruses and bacteria coming from sewages and which can be found inside the water closet (8), comprising: a container (2) containing one or more UV lamps (1) and placed inside a hole (7) obtained in the water closet (8) so that the container (2) is completely immersed in the discharge water of the syphon of the water closet (8) in order to intercept all viruses and bacteria returning from sewages and a small box containing a switching-on device and a 12/24V transformer (5) connected to the container (2) and which allows switching-on the UV lamp (1) in the syphon of the water closet (8) the container (2) is of an elongated cylindrical shape and is adapted to be inserted in the hole (7) obtained on one of the sides of the water closet (8) in order to hermetically close the hole (7).
