Objective:To develop, validate and initially apply a joint function and health assessment scale for juvenile idiopathic arthritis patients.Methods:The first draft of the juvenile idiopathic arthritis joint function and health assessment scale was developed through literature analysis, discussion by the research team, semi-structured interviews, Delphi expert correspondence. From March to June 2024, a total of 260 children with juvenile idiopathic arthritis or their parents were prospectively recruited from Department of Rheumatology and Immunology, Children′s Hospital of Chongqing Medical University by convenience sampling method for pre-investigation and formal investigation.The reliability and validity of the scale were tested by item analysis, reliability analysis, exploratory factor analysis, content validity and criterion validity analysis, and the responsiveness of the scale to clinical changes was evaluated by estimating the minimum clinically important difference, and finally the formal scale was formed.Results:The juvenile idiopathic arthritis joint function and health assessment scale included disease activity assessment, daily activity and function assessment, pain, fatigue and disease outcome assessment, with a total of 5 dimensions and 24 items, in which the functional assessment subscale included 4 secondary dimensions and 18 items. The Cronbach′s α coefficient of the function assessment subscale was 0.88, the fold-half reliability was 0.86, and the test-retest reliability after 2-4 weeks was 0.84; the item-level content validity index was 0.80-1.00, and the scale-level content validity index was 0.93. Exploratory factor analysis extracted 4 common factors with a cumulative variance contribution of 70.0%. Preliminary application indicated the functional assessment subscale was moderately correlated with childhood health assessment questionnaire ( r=0.70, P<0.05), the total scale was strongly correlated with juvenile arthritis disease activity score-27 ( r=0.92, P<0.05), and moderately correlated with both active and limited joint count ( r=0.77, 0.68, both P<0.05). Reactivity analysis suggested that the minimum clinically important difference between the two visits of 41 children with clinical improvement and 25 children with disease activity was 0.49 (0.44, 0.54) and 0.51 (0.43, 0.58). Conclusion:The juvenile idiopathic arthritis joint function and health assessment scale has good reliability and validity, and has certain responsiveness to clinical changes, is simple and operable, and can be used as a tool for assessing joint function in children with juvenile idiopathic arthritis.