Objective To investigate the value of transient elastography( FibroScan) in the diagnosis of liver fibrosis in chronic hepatitis B( CHB) children of different ages. Methods A total of 280 CHB children,aged < 18 years,who were hospitalized in The Fifth Medical Center of Chinese PLA General Hospital from June 2015 to December 2019 and planned to receive antiviral therapy were enrolled,among whom there were 157 preschool children( aged ≤6 years),74 school-aged children( aged 6-12 years),and 49 adolescents( aged 12 ～18 years). Liver biopsy was performed for all children to evaluate the degree of liver fibrosis,and according to the Matevia score,the children were divided into mild group( 0≤F < 2),moderate group( 2≤F < 3),and severe group( F≥3); FibroScan was used to determine liver stiffness measurement( LSM). LSM was compared between the children with the same degree of liver fibrosis and different ages to analyze the influence of age on LSM in judging the degree of liver fibrosis. The receiver operating characteristic( ROC) curve was used to analyze the cut-off values of LSM in the diagnosis of significant liver fibrosis( F≥2) and advanced liver fibrosis( F≥3) in children of different ages. A one-way analysis of variance was used for comparison of normally distributed continuous data between multiple groups,and the Kruskal-Wallis H test was used for comparison of non-normally distributed continuous data between multiple groups; the Wilcoxon test was used for further comparison between two groups. The chi-square test was used for comparison of categorical data between multiple groups.The Spearman rank correlation analysis was used to evaluate correlation. Results Mild liver fibrosis was found in 186 children,and LSM was 4. 9( 4. 3-5. 6) k Pa in the preschool group,5. 5( 4. 5-6. 3) kPa in the school-aged group,and 6. 0( 5. 4-7. 0) k Pa in the adolescent group,with a significant difference between the preschool group and the adolescent group( Z = 10. 929,P = 0. 003). Moderate liver fibrosis was observed in 60 children,and LSM was 5. 6( 4. 5-6. 5) k Pa in the preschool group,6. 4( 5. 4-7. 7) k Pa in the school-aged group,and 7. 1( 6. 3-8. 0) k Pa in the adolescent group,with a significant difference between the preschool group and the adolescent group( Z = 8. 517,P = 0. 011). Severe liver fibrosis was found in 34 children,and LSM was 8. 3( 7. 1-9. 2) k Pa in the preschool group,9. 1( 8. 5-13. 1) k Pa in the school-aged group,and 11. 1( 8. 5-12. 0) k Pa in the adolescent group,with no significant difference between the three groups( χ2= 4. 553,P = 0. 103). LSM was significantly correlated with the degree of liver fibrosis in the children aged ≤12 years( r = 0. 447,P < 0. 001). LSM had a cut-off value of 5. 8 k Pa and an area under the ROC curve( AUC) of 0. 74( 0. 68-0. 80) in the diagnosis of significant liver fibrosis and a cut-off value of 7. 0 k Pa and an AUC of 0. 94( 0. 90-0. 97) in the diagnosis of advanced liver fibrosis. LSM was significantly correlated with the degree of liver fibrosis in the children aged > 12 years( r = 0. 722,P < 0. 001),with a cut-off value of 6. 6 k Pa and an AUC of 0. 82( 0. 69-0. 92) in the diagnosis of significant liver fibrosis and a cut-off value of 8. 0 k Pa and an AUC of 0. 95( 0. 85-0. 99) in the diagnosis of advanced liver fibrosis. Conclusion LSM is positively correlated with the degree of liver fibrosis in CHB children,and therefore,it can be used as a noninvasive indicator for the diagnosis of advanced liver fibrosis. LSM increases with age,and the children aged > 12 years have a higher diagnostic threshold than those aged ≤12 years.