Introduction: As a “vital sign” of health and functional capacity, gait speed is commonly used. However, there is insufficient evidence for possible determinants of gait speed in patients with asthma. The primary objective of the present study was to determine predictors of gait speed in patients with asthma. The second objective was to determine the cut-off point for the 4-minute Gait Speed (4MGS) to better discriminate asthma control status and physical activity in asthma. Material and methods: Fifty-seven patients with asthma were included in this cross-sectional study. Demographic and clinic characteristics, pulmonary function, asthma control status (ACT, Asthma Control Test), dyspnea, gait speed (4MGS), physical activity [International Physical Activity Questionnaire-Short Form (IPAQ-SF)] and activities of daily living were evaluated. Stepwise multiple linear regression analysis was used to investigate the possible predictors of gait speed. Receiver operating characteristic (ROC) curve analysis was used to determine whether usual gait speed had a discriminative value. Results: The stepwise multiple regression analysis revealed that the ACT score and the IPAQ-SF score were significant and independent predictors of the 4MGS in patients with asthma explaining 40% of the variance in 4MGS (p < 0.001). The ROC curve showed a cut-off point of 1.06 m/s for the 4MGS for poorly controlled asthma and physical inactivity (p < 0.05). Conclusions: Our findings indicate that asthma control status and physical activity can be independent predictors of gait speed in patients with asthma. In addition, gait speed may be discriminative to determine poorly controlled asthma and physical inactivity in patients with asthma.