Objective To evaluate the effect of positive end-expiratory pressure (PEEP) on lung atelectasis using lung ultrasound ( LUS) in the pediatric patients without high risk factors. Methods One hundred American Society of Anesthesiologists physical statusⅠor Ⅱ patients of both sexes, aged 1-6 yr, with body mass index in the normal range, scheduled for elective non-abdominal surgery, were divided into no PEEP group (group C, n=50) and PEEP group (group P, n=50) using a random number table meth-od. The animals were mechanically ventilated in volume-controlled mode after intravenously injecting propo-fol, with PEEP 5 cmH2 O, tidal volume 8 ml/kg, inspiratory/expiratory ratio 1 : 2, respiratory rate 20-25 breaths/min in group P. In group C, the animals received no PEEP, and the other treatments were similar to those previously described in group P . Lung ultrasound was carried out after anesthesia induction and at the end of surgery. The severity and development of lung atelectasis were recorded. Results Compared with group C, the severity of lung atelectasis was significantly reduced after anesthesia induction and at the end of surgery, and the incidence of lung atelectasis was decreased in group P ( P＜0. 05) . Conclusion Early application of PEEP 5 cmH2 O can reduce the occurrence of atelectasis for the pediatric patients with-out high risk factors for atelectasis.