This report describes the perioperative anesthetic management for surgical separation of xypho-omphalopagus conjoined twins. Male conjoined twins were delivered by cesarian section after 36 weeks plus 2 days gestation. A preoperative functional evaluation was performed in assessing the feasibility of surgical separation. A partial communication of the lower margin of the sternum and a union of the livers were found but with separate biliary and vascular systems. One twin (twin-B) had a small ASD. The twins were separated at 5 days of the birth. After induction with ketamine and succinylcholine, both infants were intubated and inhalated with isoflurane, N2O and O2 respectively. Continuous arterial pressure via the femoral artery and central venous pressure via the internal jugular vein were monitored. During the induction of anesthesia, an injected bolus of ketamine and succinylcholine to one twin was not effective for the other twin. Inhaled isoflurane in one twin did not appear in the expired gas of the other twin. During the operation, the intentional hemorrhage from one twin (twin-B) caused a reduction to some degree of blood pressure and SpO2 in the other twin. We must be careful in the anesthetic management of the surgical separation of conjoined twins to consider pharmacological and cross-circulation pathophysiology.