Abstract: Objective: To evaluate the value of leukotrienes in the children with MP infection. Methods: Sixty children diagnosed with MP infection in clinical were involved as MP infection group. According to their severity, they were divided into mild infection group (n=10), median infection group (n=31) and severe infection group (n=19). Sixty healthy children with routing physical examinations in outpatient department were selected as normal control group. Both two groups were tested the serum concentration of LTB4 and the urine concentration of LTE4 by ELISA. Result: The level of serum LTB4 and urine LTE4 in the MP infection group were both significantly higher than that in the normal control group (P<0.01). There was positive correlation between the level of serum LTB4 and the urinary LTE4 in the MP infection group(r=0.522，P<0.01). There was positive correlation between the serum LTB4 and the severity in the MP infection group(rs=0.617，P<0.01) while there was positive correlation between the severity and the urinary LTE4 (rs =0.567，P<0.01). Conclusion: The level of LTB4 and LTE4 in the MP infection group was significantly high and was positive correlation with the severity in the MP infection. Leukotrienes may plays an important role in the pathogenesis mechanisms of MP infection.