Background: It has recently become most general to use the small bore catheter to perform closed thoracostomy in treating iatrogenic pneumothorax. This study was performed for analysis of the efficacy of treatment methods by using small bore catheter such as 7 F (French) central venous catheter, 10 F trocar catheter, 12 F pigtail catheter and for analysis of the appropriateness of each procedure. Materials and Methods: From March 2007 to February 2010, Retrospective review of 105 patients with iatrogenic pneumothorax, who underwent closed thoracostomy by using small bore catheter, was performed. We analyzed the total success rate for all procedures as well as the individual success rate for each procedure, and analyzed the cause of failure, additional treatment method for failure, influential factors of treatment outcome, and complications. Results: The most common causes of iatrogenic pneumothorax were presented as percutaneous needle aspiration(PCNA) in 48 cases (45.7%), and central venous catheterization in 26 cases (24.8%). The mean interval to thoracostomy after the procedure was measured as 5.2 hours (1~34 hours). Total success rate of thoracostomy was 78.1%. The success rate was not significantly difference by tube type, with 7 F central venous catheter as 80%, 10 F trocar catheter as 81.6%, and 12 F pigtail catheter as 71%. Twenty one out of 23 patients that had failed with small bore catheter treatment added large bore conventional thoracostomy, and another 2 patients received surgery. The causes for treatment failure were presented as continuous air leakage in 12 cases (52.2%) and tube malfunction in 7 cases (30%). The causes for failure did not present significant differences by tube type. Statistically significant factors affecting treatment performance were not discovered. Conclusion: Closed thoracostomy with small bore catheter proved to be effective for iatrogenic pneumothorax. The success rate was not difference for each type. However, it is important to select the appropriate catheter by considering the patient status, pneumothorax aspect, and medical personnel in the cardiothoracic surgery department of the relevant hospital.