Bitter mouth at night is often seen in oral diseases, but also related to the disease of the gallbladder. Oral diseases can also trigger bitter mouth, such as gingivitis, periodontitis or apical inflammation, which are more pronounced at night when the salivary glands produce less. Patients with burning mouth syndrome, which is characterized by dry mouth, burning sensation of the mucous membranes and abnormal taste sensation, may also experience bitter mouth at night. Bile reflux into the stomach and mouth is a common cause of bitter mouth, the vagus nerve innervates the gallbladder, in the night time the vagus nerve is excited, the gallbladder contraction accelerates the excretion of bile, at night sleeping flat on the floor to lose the factor of gravity, it is easy to lead to bile reflux into the oral cavity, all, often appear at night bitter mouth. All, the night sleep bitter mouth first to the stomatology department to exclude oral diseases, further examination needs to go to the gastroenterology or hepatobiliary surgery.