To address the reliability of CT activity score (CTAS) and investigate the relationships between CTAS, lung function changes after treatment and the serum angiotensin-converting enzyme (SACE) levels. Fifty-seven sarcoidosis patients underwent chest high-resolution CT (HRCT) and spirometry, as well as SACE examination, were retrospectively analyzed. Follow-up spirometry in each patient was obtained about 6 months after the initial spirometry. The correlations between CTAS and pulmonary function changes were evaluated by Spearman correlation analysis. According to SACE status, patients were divided into normal and high level 2 subgroups. Comparisons of pulmonary function parameters, HRCT abnormalities extent scores between SACE normal and high 2 subgroups were performed with the Mann-Whitney U test or Independent samples t test. CTAS demonstrated significant correlations with lung function changes (Delta% VC: r= 0.543, P < .001; Delta FEV1.0/FVC: rho= 0.417, P = .001; Delta% TLC: rho = 0.309, P = .019). In addition, worse initial lung function, larger changes of lung function, and higher extent scores of HRCT were observed in SACE high-level subgroup. The findings of this study suggest that CTAS of initial HRCT is a promising index for disease activity in pulmonary sarcoidosis to some degree. Prospective studies with large cohort designed to address further verification are warranted before wide clinical practice.