This study aimed to determine and compare the negative pressure in tracheal and esophageal intubation in the corpses immediately after the end of cardiopulmonary resuscitation. The current cross-sectional study was conducted in the emergency departments of Imam Reza and Ghaem hospitals in Mashahd, Iran, in 2021 and 2022. The target population consisted of patients who had undergone unsuccessful cardiopulmonary resuscitation and had died. After obtaining consent from the families of the patients who died in the emergency department. We included their bodies in the study immediately at the end of the unsuccessful cardiopulmonary resuscitation. Exclusion criteria included confirmed oesophageal disease or musculoskeletal disorders. To record the pressures, we simultaneously placed the tracheal tube in the oesophagus and trachea, and the negative pressure inside them was measured by a manometer connected to the suction device, and then the pressure inside the oesophagus and trachea of the corpses was recorded. A total of 30 corpses were examined, among which 20 were male (66.7%) and 10 (33.3%) were female. Their mean age was equal to 49.86 ± 19.97 years with the range of 23 to 78 years. The average negative pressure of the oesophagus was 494.00 ± 13.66, and the average negative pressure of the trachea was 319.60 ± 14.59. The maximum and the minimum negative pressures of the oesophagus were 479 and 553, respectively, and those of the trachea were 290 and 343. There was a significant difference in terms of negative pressure between the oesophagus and trachea (p<0.001). In general, the negative pressure of the oesophagus was significantly higher than that of the lungs. This can be used in future studies to attain a correct diagnostic method to differentiate correct endotracheal intubation from oesophageal intubation.