Abstract: Objective To compare the safe duration of apnea and intubation time between face mask ventilation with air and 100% oxygen during induction of general anesthesia. Methods Eighty adult patients with ASA class I or II without predicted difficult airways were scheduled for elective surgery under general anesthesia. The patients were randomized to receive anesthesia induction with preoxygenation [Group 1, n=40, fraction of inspired oxygen (FiO2) =1] or without preoxygenation (Group2, n=40, FiO2=0.21). Two experienced anesthesiologists performed the mask ventilation and tracheal intubation during induction, and the assistants adjusted the oxygen concentration and recorded the pulse oxygen saturation (SpO2) and other variables. The cases where SpO2 decreased to below 90% before accomplishment of intubation were considered unsuccessful, and mask ventilation with 100% oxygen was given. After tracheal intubation, mechanical ventilation was not initiated until the SpO2 decreased to 90%. The number of unsuccessful cases, the safe duration of apnea and intubation time were recorded in the two groups. Results There was no unsuccessful case in either groups. The safe duration of apnea was 469.5±143.0 s in Group 1 and 63.6±20.0 s in Group 2, and the intubation time was 34.4±12.6 s and 32.8±9.6 s, respectively. The safe duration of apnea was significantly longer than the intubation time in both groups (P<0.01). The intubation time and the number of cases with SpO2≥ 90% before completion of tracheal intubation were similar between the two groups. The safe duration of apnea was significantly shorter in Group 2 than in Group 1 (P<0.01) and was correlated with the body mass index of the patients (P<0.05). Conclusion Anesthesia induction without preoxygenation can provide sufficient time for experienced anesthesiologists to complete tracheal intubation.