A 68 years old male patient was scheduled for open cholecystectomy and common bile duct exploration for gallstone and common bile duct stones with cholecystitis. With the patient in lateral decubitus position, a 17 G Tuohy needle was inserted into the epidural space via midline approach at the T10-11 interspace by using the loss of resistance technique. Then, an 18 G epidural catheter was inserted into the epidural space upward 5 cm for postoperative pain control without complications such as bleeding, paresthesia or CSF leakage. After the epidural catheterization, general anesthesia was induced. During the surgery, the aspiration test via the epidural catheter was done once more before connection of PCA device to the epidural catheter, and some clear fluid was found to be aspirated. Intrathecal migration of the epidural catheter was doubted and confirmed by a measurement of glucose level and the thiopental precipitation test. After the end of surgery, the epidural catheter was removed and the patient was discharged from the PACU 1 hour later without any complication or sequelae. We report a case of early detection of intrathecal migration of an epidural catheter by a measurement of glucose level and the thiopental precipitation test of the aspirated fluid.