INTRODUCTION: Obesity can adversely impact respiratory function and limit physical activity (PA). Sleeve gastrectomy (SG) is an essential and uptrend treatment option for weight loss. However, the effect of SG on pulmonary function and PA in patients with obesity is still debated. METHOD: This is an observational study of 32 cases with obesity (BMI 43.86 ± 4.39) who underwent SG in a single center. Spirometry was performed before and 12 months after SG to investigate the pulmonary function of individuals. The main variables were forced expiratory volume (1s) (FEV1), Forced vital capacity (FVC), FEV1/FVC ratio, and maximum inspiratory pressure (MIP). The correlation of weight loss variables with findings was evaluated. RESULT: One year after surgery, patients lost an average of 23.42 kg (P <
.002). The FEV1 and FVC were increased by 0.22 ml and 0.38 ml, respectively (p <
.002). The absolute changes in FEV1 and FVS were significantly correlated with Total weight loss percentage (TWL). The 6-minute walking test (6MWT) results were significantly increased after surgery by 53.71 m (p <
.002), and changes were correlated with TWL. CONCLUSION: More than significant weight loss, the SG can also significantly improve the respiratory function and PA of individuals with obesity 12 months after surgery. Additionally, there was a positive correlation between weight loss and modification in lung function tests. The findings required studies with larger sample sizes and longer follow-up times to confirm and clarify.