Resuscitation bag (RB) is widely used for artificial ventilation and adequate ventilation during resuscitation, or for patient transport, when high concentration of inspired oxygen (70-100%) must be supplied. The purpose of this study was to investigate the effect of oxygen flow and the length of corrugated tube as a reservoir on the oxygen concentration in the adult type and pediatric type resuseitation bag. Each 24 mm corrugated tube (0, 20,40, 60, 80, 100 cm) was attached to the inlet valve, oxygen flow of 1, 3, 5, 7, 9, 11, 13 or 15 L/min was delivered to oxygen inlet site of RB. and oxygen concentration was measured for 10 times. To eliminate the possibility that ventilatory pattern affect the oxygen concentration, RB was manually handled with normal ventilatory pattern ; in advlt type, tidal volume was 800 cc, respiratory rate was 10/min and 1:E ratio was 1:2, in pediatric type, tidal volume was 100 cc, respiratory rate was 20/min and 1:E ratio was 1:2. In adult RB, a 15 L oxygen flow without reservoir delivered less than 50% oxygen. To get more than 70% oxygen, one must administer more than a 15 L oxygen flow with reservoir of 60 cm corrugated tube, oxygen flow of 9 L/min with 80 cm corrugated tube or a 7 L flow of oxygen with 100 cm corrugated tube. And to provide more than 80%, oxygen of more than a 11 L flow with reservoir of 100 cm should be delivered. In pediatric RB, a 15 L oxygen flow without reservoir get more than 70% oxygen. A 20 cm corrugated tube as a reservoir increased abruptly oxygen concentration, and A 40 cm tube with more than a 7 L flow delivered more than 95% oxygen, but above 60cm tube there is little increase in the oxygen concentration. These results indicated that to get more than 70% oxygen, 60 cm and 40 cm corrugated tube is required in adult type RB and pediatric type RB respectively as an oxygen reservoir.