Objective: To investigate the relationship between the changes of serum and urine beta2-microglobulin (beta2-MG) in children with pneumonia and the renal impairment, and to explore the sensitive index for early diagnosis of renal injury., Methods: The contents of serum and urine beta2-MG were determined with radio immunoassay in 145 cases with pneumonia at the stages of acute and convalescence and 82 healthy controls, serum creatinine (SCr) and blood urea nitrogen (BUN) were also determined at the same time., Results: The contents of serum and urine beta2-MG in children with pneumonia at the stages of acute were significantly higher than those in controls (both P<0.01), and compared with convalescence, there was a significant difference (both P<0.05). There was no significant difference between the convalescence and healthy control groups. There were found to have a significant difference in these data between attack and interval stages, and mild and severe pneumonia in children (both P<0.05). At the same time, the study showed that there was significant positive correlation between serum beta2-MG and BUN or SCr in children with pneumonia (r(BUN)=0.635, r(Cr)=0.621; both P<0.05). The abnormal rate of serum beta2-MG at the acute stages was markedly higher than that of SCr and BUN., Conclusion: The major characteristics of children's pneumonia is a reversible renal injury, which is a widespread pneumonia to be following in children with pneumonia and it is more significant in severe pneumonia. Serum and urine beta2-MG can be a sensitive index of monitoring the kidney involvement at early stage of pneumonia in children.