The most commonly used open circuit is The Jackson Rees modification of the Ayre's T-piece (Mapleson-F system) in pediatric patients because it has low resistance and nominal dead space. Here, we report a case in which we used the Jackson Rees circuit with bag tail valve for ventilation in pediatric patient weight 12 kg. During positive-pressure ventilation, we felt resistance and the patient was not ventilating. High pressure in the bag was being formed despite the valve was fully open. On inspection, we found out the cause was a twisted bag tail end as shown in Figure 1. We straighten the tail end of the bag, which aided in releasing air pressure and the patient started getting ventilation. The obstruction of the expiratory limb of the reservoir bag may be due to a stuck valve or due to twisting of its tail end. Due to high flexibility, twisting of the tail end of reservoir bag commonly found when it was held with tail end up position. Due to the twisting of the tail end of the reservoir bag, the expiratory limb becomes closed and high flow oxygen started going to the inspiratory limb. This may result in CO₂ retention and barotraumas of the lungs if the obstruction was not released. We can prevent twisting of the tail end of the bag by keeping the Jackson Rees circuit in a vertical position with the tail end facing down.