Roles of lung volumes in asthma remain controversial. We aimed to evaluate the efficacy of lung volumes in differentiating asthma severity levels. Consecutive outpatients with chronic persistent asthma were enrolled, and body plethysmography (BP) and helium dilution (HD) were performed simultaneously to extract RV% pred, TLC% pred, and RV/TLC. Significant negative correlations were found between FEV1% pred and RV% pred (r = -0.557, P < 0.001), TLC% pred (r = -0.387, P < 0.001), and RV/TLC (r = -0.485, P < 0.001) measured by BP, as well as difference in volumes between these two techniques (Delta RV% pred, Delta TLC% pred and Delta RV/TLC). In mild and moderate asthma, AUC of RV% pred detected by BP and Delta TLC% pred was 0.723 (95% CI 0.571-0.874, P = 0.005) and 0.739 (95% CI 0.607-0.872, P = 0.002) with sensitivity and specificity being 79.41% and 88.24%, and 65.22% and 56.52% at cut-off of 145.40% and 14.23%, respectively. In moderate and severe asthma, AUC of RV% pred detected by BP and Delta TLC% pred was 0.782 (95% CI 0.671-0.893, P < 0.001) and 0.788 (95% CI 0.681-0.894, P < 0.002) with sensitivity and specificity being 77.78% and 97.22%, and 73.53% and 52.94% at cut-off of 179.85% and 20.22%, respectively. In conclusion, lung volumes are reliable complement of FEV1 in identifying asthma severity levels.