OBJECTIVE: To study the etiology of acute lower respiratory infection (ALRI) in children. METHODS: The multiple pathogens of 246 cases of ALRI were studied by the culture of bacteria and Mycoplasma pneumoniae of sputum and the methods of alkaline phosphatase anti alkaline phosphatase (APAAP) and ELISA. RESULTS: Of the 246 patients with ALRI, 50.4% were viral infection, 4.1% were due to bacterial infection and 27.2% were viral mixed with bacterial infection. The incidence of Mycoplasma pneumoniae infection was 5.7% and unknown pathogens were approximately 12.6%. There was no simple bacterial or Mycoplasma pneumoniae infection in the bronchiolitis group, and no simple bacterial infection in the bronchitis group was found either. The rate of mixed infection in the under 1 year old patients was higher than that in the over 1 year old group (χ2=13.77,P<0.05).The level of serum Creactive protein (CRP) in children with bacteria infection was higher than that in children with viral infection (χ2=34.44，P<0.05).CONCLUSIONS: Viral and mixed infections are prominent pathogens of ALRI. Mixed infection is the most common in infants with ALRI. CRP estimation may be helpful in distinguishing bacterial infection from viral infection early.