Background: Postoperative pulmonary complications and pain are important causes of postoperative morbidity following thoracotomy. This study aimed to compare the effects of fast track and conservative treatment regimens on patients undergoing thoracotomy. Materials and Methods: In this randomized controlled clinical trial, we recruited 60 patients admitted to the thoracic ICU of Imam Reza Hospital in two matched groups of 30 patients each. Group 1 patients received fast track regimen randomly; whereas, group 2 cases randomly received conservative analgesic regimen after thoracotomy and pulmonary resection. The outcome was determined based on the incidence of pulmonary complications and reduction of post-thoracotomy pain in all patients with forced expiratory volume in one second (FEV1) <75% predicted value which was measured while the patients were in ICU. The length of ICU stay, thoracotomy pain, morbidity, pulmonary complications and mortality were compared in two groups. Results: A total of 60 patients, 45 (75%) males and 15(25%) females with ASA class I-III were recruited in this study. Postoperative pulmonary complications were observed in 5 (16.7%) patients in group 1 versus 17 (56.7%) patients in group 2. There were statistically significant differences in development of postoperative pulmonary complications such as atelectasis and prolonged air leak between both groups (p < 0.001 and P=0.003). There was also a statistically significant difference in the rate of preoperative FEV1 (p=0.001) and ASA scoring (p=0.01) and value of FEV1<75% predicted in the two groups. The difference in length of ICU stay in two groups was statistically significant (P= 0.003 and P=0.017 in FEV1<75% group). Four patients in group 1 and 9 patients in group 2 had FEV1reduced to less than 75% of predicted value (p=0.03). Conclusion: Using fast track regimen reduced postoperative pain and incidence of some pulmonary complications significantly when compared to the conservative regimen following thoracotomy and various lung surgeries. (Tanaffos2011; 10(3): 12-19)