Background: Adaptive support ventilation (ASV), an automated closed-loop ventilation mode, adapts to the mechanical characteristics of the respiratory system by continuous measurement and adjustment of the respiratory parameters. The adequacy of ASV was evaluated in the patients with acute lung injury (ALI). Methods: A total of 36 patients (19 normal lungs and 17 ALIs) were enrolled. The patients` breathing patterns and respiratory mechanics parameters were recorded under the passive ventilation using the ASV mode. Results: The ALI patients showed lower tidal volumes and higher respiratory rates (RR) compared to patients with normal lungs (7.1±0.9 mL/kg vs. 8.6±1.3 mL/kg IBW; 19.7±4.8 b/min vs. 14.6±4.6 b/min; p＜0.05, respectively). The expiratory time constant (RCe) was lower in ALI patients than in those with normal lungs, and the expiratory time/RCe was maintained above 3 in both groups. In all patients, RR was correlated with RCe and peak inspiratory flow (rs=-0.40; rs=0.43; p＜0.05, respectively). In ALI patients, significant correlations were found between RR and RCe (rs=-0.76, p＜0.01), peak inspiratory flow and RR (rs=-0.53, p＜0.05), and RCe and peak inspiratory flow (rs=-0.53, p＜0.05). Conclusion: ASV was found to operate adequately according to the respiratory mechanical characteristics in the ALI patients. Discrepancies with the ARDS Network recommendations, such as a somewhat higher tidal volume, have yet to be addressed in further studies.