PURPOSE: The purpose of this study was to develop the instrument to measure family functioning for Korean family with a chronic ill child, and to test the validity and reliability of the instrument. METHOD: The items of instrument were consisted based on researchers' previous study of concept analysis of the Korean family functioning. Twenty six item scale was developed with six domains. In order to test reliability and validity of the scale, data were collected from the 231 families, who have a child with a chronic illness. Data was collected between August and September in 2001 in a General Hospital in Seoul, Korea. RESULT: The results were as follows:As a result of the item analysis, 24 items were selected from the total of 26 items, excluding items with low correlation with total scale. Six factors were evolved by factor analysis. Six factors explained 61.4% of the total variance. The first factor 'Affective bonding' explained 15.4%, 2nd factor 'External relationship' 11.8%, 3rd factor 'Family norm' 10.5%, 4th factor 'Role and responsibilities' 8.3%, 5th factor ' Communication' 7.9%, and the 6th factor 'Financial resource' explained 7.3%. Cronbach's alpha coefficient of this scale was .87 and Guttman spilt- half coefficient was .84. CONCLUSION: The study support the reliability and validity of the scale. There were distinct differences in dimensions of family functioning scales developed in the U. S.