Objective To investigate the clinical significance of serum level of the diagnosis and treatment of community acquired pneumonia. Methods 42 hospital patients with pneumonia obtained from community were slected as the observation group.According to patient outcome, they were divided into improvement group and aggravated group. Another selection during the same period in hospital for treatment of acute upper respiratory tract infection in patients with 30 cases was the control group. Respectively, in the 1 day,3 days,7 days the results of serum calcitonin angiotensinogen(PCT)and CRP were compared and analyzed. Results In observation group,PCT of first day,third days and seventh days were respectively(1.18±0.32)μg/L,(0.78±0.12)μg/L and(0.18±0.04)μg/L;CRP were respectively(154.15±21.58)mg/L,(67.42±20.35)mg/L and(15.43±7.76)mg/L.In the control group,PCT of first days,third days and seventh days were respectively(0.05±0.01)μg/L,(0.04±0.02)μg/L and(0.05±0.02)μg/L,while CRP were respectively(9.39±2.22)mg/L,(8.83±2.91)mg/L and(7.06±3.03)mg/L. There were significant differences between the two groups(t=6.15,10.85,4.86,58.69,16.79,11.99, all P<0.05).In the aggravated group,PCT levels of first days,third days and seventh days were significantly higher than that of the improved group, the differences were statistically significant(t=17.86,18.21,20.65,all P<0.05). Conclusion As a monitoring marker,PCT showed higher sensibility and specificity than CRP in diagnosis and treatment of CAP, and it would be helpful to make early diagnosis and certain the therapeutic schedule to use antibiotics. Key words: Procalcitonin; C-reaction protein; Community acquired pneumonia