Objective: To evaluate respiratory function in the post-operative early period of patients undergoing bariatric surgery using the sleeve gastrectomy technique. Methods: This prospective, observational study was conducted at Bulent Ecevit University Health Application and Research Centre, Zonguldak, Turkey from June to December 2014, and comprised patients with planned bariatric sleeve gastrectomy under general anaesthesia. Participants were visited 12-24 hours before the operation to record accompanying diseases and demographic data. Before the operations, respiratory function test, maximum expiratory pressure, maximuminspiratory pressure and arterial blood gas assessment tests were done and recorded as T0. After one hour of the operation, Aldrete scores >= 9 and the above-mentioned tests were repeated and recorded as T1. SPSS 18 and MedCalc 12.2.1.0 were used for statistical analysis. Results: Of the 76 participants, 60(78%) were women and 16(21%) were men. The overall median age was 39 years (inter-quartile range: 32-47 years). The mean and median values for forced expiratory volume in 1 second, forced vital capacity, maximum inspiratory pressure, maximum expiratory pressure and the ratio between partial pressure of oxygen in arterial blood and fraction of inspired oxygen at T0 were 101 +/- 17, 102 +/- 17, 66 (interquartile range: 5974), 114 (interquartile range: 100-138) and 379 +/- 49, respectively, compared with 78 +/- 18, 76 +/- 18, 53 (interquartile range: 48-59), 85 (interquartile range: 73-95) and 331 +/- 49 at T1 (p< 0.001 each). Also, 38(50%) participants were given sugammadex and 38(50%) were given neostigmine. At the end of the test, sugammadex (odds ratio: 5.80; 95% confidence interval: 1.26-26.69; p= 0.024) and pre-operative ratio between partial pressure of oxygen in arterial blood and fraction of inspired oxygen (odds ratio: 1.04, 95% confidence interval: 1.02-1.06; p< 0.0001) were found to correlate significantly. Conclusion: Impairment of respiratory function was found during the early post-operative period.