Objective：To analyze the clinical characteristics of children with bloody pleural effusion. Methods：The clinical data of 21 children with bloody pleural effusion from June 2004 to May 2014 were retrospectively analyzed，including clinical manifestations，auxiliary examination（B ultrasound，CT，pleural effusion and bone marrow examination） and the treatments. Results：Among 21 cases，8 cases are caused by bacterial infection，7 caused by mycoplasma pneumoniae infection，3 caused by lung trematode infection，1 caused by tuberculosis infection，1 caused by acute leukemia，and 1 caused by unknown aetiology. There were 2 positive cases in the pleural effusion bacterial culture. The eosinophils of 3 cases were very high （37%~61%），and the mycoplasma PCR of 4 cases were positive in the pleural effusion check. One acute leukemia case was confirmed by bone marrow check. All cases were cured except the acute leukemia case and the case caused by unknown aetiology. Conclusion：Most cases of bloody pleural effusion are caused by in－fection，mainly bacteria infection and mycoplasma pneumoniae infection.