Objective To investigate the changes of serum adiponectin (APN) level in the elderly patients with pulmonary infection and its relationship with C-reactive protein (CRP), in order to provide basis for clinical diagnosis and disease monitoring for these elderly patients. Methods A total of 70 elderly patients with pulmonary infection admitted in our hospital from January 2012 to June 2013 were enrolled in this study. They were divided into severe pulmonary infection group (n=30) and mild pulmonary infection group (n＝40). Another 40 elderly receiving physical examination in the same period served as controls. ELISA and immune turbidimetry were used to detect the serum levels of APN and CRP respectively. Results The serum levels of APN were significantly lower in the mild and severe pulmonary infection groups than in the controls [(6.79±1.87) and (4.89±1.13) vs (8.89±1.93)mg/L; P＜0.05], but that of CRP was significantly increased [(13.87±2.72) and (25.73±5.77) vs (1.69±1.12)mg/L; P＜0.05]. A negative correlation was found between the serum levels of CRP and APN in the elderly patients with pulmonary infection (r＝-0.350; P＜0.05). Logistic regression analysis showed that APN (OR＝0.350, 95% CI 0.225?0.544; P＜0.05), fasting blood glucose (OR＝3.939, 95% CI 1.066?14.552; P＜0.05), and age (OR＝0.870, 95% CI 0.781?0.969; P＜0.05) were correlated with pulmonary infection in the elderly. Conclusion Serum level of APN is decreased significantly in the elderly patients with pulmonary infection. It may be a new anti-inflammatory factor, and can be used as a new marker for diagnosis and disease monitoring of pulmonary infection in the elderly.