This paper deals with the effect of pyloroplasty on the motility of the stomach observed by the use of electromyography. Twenty adult dogs were subjected to the Heineke-Mikulicz type pyloroplasty and the electromyographical study was carried out on the motility of the stomach following the operation. When the pyloroplasty was done on the normal stomach, peristaltic movement of the stomach was seen slightly weakened. Transection and anastomosis of the body or antral portion of the stomach was followed by the increase in peristaltic movement distal to the anastomotic line and the multiple discharges of the antiperistalsis were also observed. Under these conditions, addition of the pyloroplasty remarkably reduced the discharge of antiperistalsis. It is presumed that the clinical significance of the pyloroplasty as an additional procedure to vagotomy or various kinds of gastric surgeries is the reduction of abnormally excited condition of the antrum as well as antral spasm and antiperistalsis.