Background: Soluble CD14 (sCD14) shedding from CD14 could regulate T lymphocyte activation and function, which has implicated in the pathogenesis of bronchial asthma. The level of sCD14 expression is obviously increased in asthmatic patients during acute asthma attacks. The objective of this study was to investigate the association between plasma sCD14 level and asthma severity in adults. Methods: The plasma sCD14 level in asthma patients (n = 910) and healthy controls (n = 881) was quantified by commercially available enzyme-linked immunosorbent assay (ELISA) kits. The asthma cases were subdivided into intermittent asthma (n = 537), mild (n = 246), moderate (n = 96) and severe (n = 31) persistent asthma patients. Association between plasma sCD14 level and asthma severity, lung function parameters as well as asthma symptoms and signs in adults were performed using multivariate logistic regression models. Results: We observed significant relationships of plasma sCD14 level with asthma severity, lung function parameters as well as asthma symptoms and signs in adults. After adjusting for multiple potential confounders, each one-unit increase in log sCD14 was significantly associated with 67, 82, 79 and 85% reduced ORs for intermittent asthma, mild, moderate and severe persistent asthma, respectively (all P < 0.0001). Compared with the participants of FEV1/FVC >= 75%, each one-unit increase in log sCD14 was significantly associated with a 37% decreased OR of FEV1/FVC < 75% (P < 0.0001). However, the adjusted odds ratios (ORs) of severe dyspnea, wheeze and cyanosis in asthma patients were 1.88, 1.46 and 2.20 for each one-unit increase in log sCD14, respectively. In addition, compared with health controls, the adjusted area under the curve (AUC) of sCD14 was 0.814 at a cut-off points of 0.53, and the sensitivity and specificity were 71.0 and 76.8% for predicting asthma in adults. And the adjusted AUC of sCD14 reached 0.786, 0.847, 0.887 and 0.917 in predicting intermittent asthma, mild, moderate and severe persistent asthma, respectively. Conclusions: Our results indicated that plasma sCD14 level is negatively associated with asthma severity, suggesting a protective role for sCD14 in the development of asthma in adults. And plasma sCD14 level might be a potential biomarker in prediction of asthma severity in adults.