Objective To explore the early diagnosis value of serum procalcitonin (PCT) and Creactive protein (CRP) on lower respiratory tract diseases.Methods Two hundred patients with lower respiratory tract diseases were selected as our subjects.Serum PCT and CRP levels were measured and analyzed before and after treatment.Results Serum PCT of 90 patients with bacterium infection before and after treatment were (4.23 ± 3.48) μg/L and (1.90 ± 0.90) μg/L respectively; and serum CRP were (62.38 ± 17.13) mg/L and (9.55 ±3.52) mg/L.Serum PCT and CRP of the patients with bacterium infection after treatment were statistically different from that before treatment (t =6.149,29.96 ; P ＜ 0.01).Serum PCT and CRP of patients with bacterium infection was statistically different from those of patients with virus infection or no infection(F =41.04,12.89 ;P ＜ 0.01).Conclusion Serum PCT and C-reactive protein show significant value in early diagnosis in lower respiratory tract infection.Dynamically testing them will help to assessment of curative efficacy.