Researchers have used various techniques to form pneumothorax in animals, but to date, no standard method or rate of pneumothorax has been defined. We tried to develop a standard and a safe method of pneumothorax model in this study. 12 female Wistar Albino rats weighing 200-220 g were used. Two groups (6 rats in each) were formed. Open pneumothorax was formed by 0.5 cm incision through the right, 5(th) intercostal space. The first group was held in open pneumothorax position for 1 min and the second group, for 2 min and the incisions were sutured. After 48 h, computed tomography of the rats were obtained and the pneumothorax rates were measured. The mean pneumothorax value was greater in Group II (13.89%) than in Group I and it was statistically significant (p < 0.05). The above mentioned method produces low rates of pneumothorax (10 - 15%), without injuring lung tissue. It should be useful for researchers, who plan to study lung physiology with low rates of pneumotohorax.