A bug zapper includes a body, a fan and a light source. The body has a compartment, an opening, a channel arranged between the compartment and the opening, and a coupling portion arranged between the compartment and the channel. The channel is formed by an enclosed reflection wall and gradually expands from the coupling portion towards the opening. The fan is coupled with the coupling portion. The light source is mounted on a location of the body adjacent to the fan and irradiates light in the channel. As such, the efficiency in attracting the mosquitoes is outstanding, and the negative effect to the human is reduced.