This study was undertaken to observe whether an adult ventilator with a preset volume could be used as a controlled ventrolled ventilator far pediatric anesthesia. 35 Patients ranging in age from 3months to 7 years were divided into two groups based on body weight(Group 1: 5~10kg, 14 cases, Group 2: 11~15kg, 21 cases) and anesthetized with halothane-N2O/O2 - pancuronium using the Mapleson B system. Immediately after induction, the reservoir bay of the Mapleson B system was replaced by the reservoir tube of the adult ventilator (MCM 801). Arterial blood gas studies 30 and 60 minutes after induction were performed, and the data from group 1 was compared with that of group 2. The magnitude of PCO2 increase 30 minutes after induction was not significantly different from that at 60 minutes(p>0.05), and alterations of PCO2 in group 1 were not stati-stically significant with group 2 (P>0.05). In conclusion, it is suggested that the Mapleson B system attached to adult ventilator is an useful and convenient device for controlled ventilation in pediatric patients.