The present invention relates to a toothbrush and provides an electric toothbrush comprising a hollow hand-held casing; the hand-held casing is disposed therein with a rechargeable lithium battery via a battery mount, and a brushless motor via a motor mount. The battery mount accommodates a PCT connected with the rechargeable lithium battery. The PCB is disposed with a control switch via a waterproof mount and a waterproof switch case. The press portion of the control switch is exposed from the switch hole of the hand-held casing. The vibration shaft of the brushless motor passes through the motor mount to an exterior of the hand-held casing. The vibration shaft is connected to a toothbrush head. The hand-held casing is threadedly connected to the rear cap at a bottom end thereof. The hand-held casing has a cross section in shape of a circle.