Spontaneous gastric perforation of the newborn is a rare, serious and life-threatening problem. This is surgical emergency because of high mortality. Most historical reports have described gastric perforation in the neonate as spontaneous cause. But, recent reviews report the contributing factor including prematurity and mechanical ventilation. Usually clinician identifies the pneumoperitoneum in simple abdomen X-ray. The final diagnostic method is surgical finding and the treatment of gastric perforation is immediate surgical correction. Early diagnosis, hemodynamic monitoring and fluid therapy for hypovolemia improve outcome. Pseudocyst formation after gastric perforation is very rare in newborn. We report a rare case of pseudocyst formation after spontaneous gastric perforation in full term newborn.