[Purpose] The purpose of our study was to investigate the effect of different positions on pulmonary function test (PFT) values such as forced vital capacity (FVC) and forced expiratory volume in one second (FEV₁) of asthmatic patients .[Subjects and Methods] Thirty subjects with severe asthma aged between 20–39 years were enrolled after they had signed a written consent. Subjects were selected using the inclusion criteria, and PFT were randomly administered. Spirometer measurements (FVC, FEV₁) were taken in the supine, side lying on right, side lying on left, sitting and standing positions. Each measurement was taken three times, and the average values were analyzed. [Results] One- way analysis of variance (ANOVA) and Tukey’s Test (post hoc) for pair- wise comparison indicated that there was a significant difference in the FEV₁ values of the asthmatic patients however a significant difference was obtained between standing and supine positions. There was also a significant difference in the FVC values between the standing and supine lying position in the pair -wise comparison. [Conclusion] This study showed standing is the best position for measuring FEV₁ and FVC of asthmatic subjects. The more upright the position, the higher the FEV₁ and FVC will be.