Abstract: Objective: To analyze the etiology and clinical characteristics of children with bloody pleural effusion(BPE). Methods: Retrospective collection of BPE children admitted to Shenzhen Children’s Hospital was performed from June 1st, 2009 to June 30th, 2019. The clinical manifestations, imaging examination (B-ultrasonography, chest CT), fiberoptic bronchoscopy, bone marrow cytology, routine biochemistry of pleural fluid, etiological examination, treatment and outcome of the cases were collected. Results: During the study period, there were a total of 1,416 children with pleural effusion in our hospital, among whom 26 BPE children (1.8%) were included in our study. They were aged from 3 months to 13 years and 11 months, and all had a history of BCG vaccination. The course of disease ranged from 4 h to 25 d. Among them, 18 cases were caused by infection and 11 cases were identified as mycoplasma infection (4 cases), pseudomonas aeruginosa (2 cases), streptococcus pneumoniae (1 case), aspergillus fumigatus (1 case), tuberculosis bacillus (1 case), cytomegalovirus (1 case) and EB virus(1 case). There were 7 cases with unknown pathogens, 7 cases with tumors and 1 case with unknown etiology. The onset was mainly featured by fever (16 cases), cough (11 cases), shortness of breath (8 cases), dyspnea and chest pain (3 cases each). Chest B-ultrasound showed medium volume pleural effusion in 13 cases, massive volume pleural effusion in 11 cases and enveloping effusion in 2 cases. Chest CT showed bilateral pleural effusion in 10 cases, unilateral pleural effusion in 16 cases, combined with pneumothorax in 3 cases, necrotic pneumonia in 2 cases and pericardial effusion in 2 cases. Fiberbronchoscopy was performed in 8 patients, and pathogen of alveolar lavage fluid was positive in 5 patients with 3 cases of mycoplasma DNA, 1 case of aspergillus fumigatus, 1 case of pseudomonas aeruginosa. Bone marrow cytology was performed in 5 cases, including 1 patient with dysplastic bone marrow (acute myelogenous leukemia) and 1 patient with haemophilic cells. Blood culture and/or sputum culture were conducted in 22 cases, including 3 positive cases, 1 case of Pseudomonas aeruginosa (blood culture), 1 case of Pseudomonas aeruginosa (blood and sputum culture) and 1 case of Streptococcus pneumoniae (sputum culture). The etiology of pleural fluid was examined in all cases and 7 cases were positive (mycoplasma PCR positive in 3 cases, EBV DNA positive in 1 case, Pseudomonas aeruginosa in 2 cases, Streptococcus pneumoniae in 1 case). Two patients (1 with combined immunodeficiency and 1 with T-lymphoblastic lymphoma) died and other patients were discharged with improved condition after anti-infection or chemotherapy treatments. Conclusion: Most cases of BPE were caused by infection in children, followed by malignant tumors that large or medium quantities of pleural effusion were predominant.