Background: Surgical hyperaldosteronism leads to sodium and water retention during surgery and often causes postoperative edema. This study investigated the effect of potassium canrenoate (PC) on pituitary adrenocortical function in lower abdominal surgery under sevoflurane anesthesia. Methods: Twenty patients were randomized to receive 400 mg of PC (the PC group, n=10) or saline (the control group, n=10) intravenously. The following parameters were determined: plasma aldosterone, adrenocorticotropic hormone (ACTH), plasma renin activity (PRA), serum sodium and potassium, urinary sodium and potassium, and urine output. Results: The aldosterone and ACTH levels showed significant increases in the control group during surgery. Plasma ACTH also increased significantly in the PC group, but plasma aldosterone levels were unchanged during surgery. The urine Na/K ratio of the PC group was significantly higher than that of the control group. Conclusion: The present study suggested that PC suppresses the increase of plasma aldosterone caused by surgical stress. That may prevent sodium retention and potassium excretion during surgery.