Abstract: Objective To evaluate the usefulness of the serum procalcitonin (PCT) level as a predictor of diagnosis in elderly patients with pneumonia and to discuss the value of the serum PCT in the severity assessment of bacterial pneumonia. Methods A total of 314 pneumonia patients were respectively reviewed and assigned into bacterial pneumonia group (121 cases), viral pneumonia group (97 cases) and mycoplasma pneumonia group (96 cases) according to the diagnostic criteria for pathogens causing pulmonary infections treated from January, 2015 to June, 2016 in our hospital, and100 healthy elderly healthy people without infection at the same period were selected as the control group. The 121 bacterial pneumonia patients were grouped according to the severity of illness. All patient groups and control group were respectively detection PCT and CRP in serum. PCT and CRP contents in patients of each group were summarized and data were processed by statistical software SPSS 17.0. Results The levels of PCT and CRP in bacterial pneumonia group were significantly higher than viral pneumonia group, mycoplasma pneumonia group and control group (P<0.05); the level of PCT and CRP increased along with the severity of bacterial pneumonia. The threshold of PCT and CRP were 0.5μg/L and 10 mg/L, respectively. The sensitivity of the serum PCT and CRP were 90.9% and 86.8%, respectively, the sensitivity is no statistical different (P>0.05); the specificity of the serum PCT and CRP were 90.4% and 77.5%, respectively, the specific of serum PCT is obviously higher than that CRP (P<0.01). Conclusion PCT may have a role to predict the etiological diagnosis in patients and the severity in the bacterial pneumonia. The specific of serum PCT in the diagnosis of bacterial pneumonia was obviously higher than that of serum CRP.