A nebulizer including a host having a head portion, a cup body having a nebulizing module disposed on a bottom thereof, an engaging member, a mouthpiece having a first opening, a second opening, and a tongue plate, and a sensor element is provided. The engaging member includes a first, a second, and a third engaging opening communicated with one another. The cup body is coupled to the engaging member through the first engaging opening. The engaging member, inside which a first partition wall is disposed, is coupled to the host through having the third engaging opening engaged with the head portion. The mouthpiece is coupled to the engaging member through having the second opening engaged with the second engaging opening. The tongue plate, disposed inside the mouthpiece and abuts against the first partition wall, divides an inner space of the mouthpiece into a first and a second channel.