--- - |2 Abstract The cognitive behavioral approach for families of individuals with hikikomori (IWH) places importance on assessing family interaction from a behavior theory. However, there is no gold standard method for the assessment of family interaction of IWH. Additionally, the characteristics of the family interactions of IWH have not been clarified. This study aims to (a) develop the Family Interaction Scale for Hikikomori (FIS‐H) using parent‐reported data, and (b) clarify the characteristics of hikikomori cases. First, the FIS‐H factor structure was examined. Second, to examine the reliability and validity of the FIS‐H and the characteristics of hikikomori cases, parents of IWH (hikikomori‐group) and unaffected parents (without‐group) completed the FIS‐H and the Relationship Happiness Scale. Based on data from 146 parents, the FIS‐H preliminary version consisted of four factors with a total of 12 items (Study 1). The reliability and validity of the FIS‐H were also confirmed to be acceptable using data from 246 hikikomori‐group participants. The hikikomori‐group had higher FIS‐H scores than did the without‐group (Study 2). These results show that it is important to appropriately assess family interactions. - Japanese Psychological Research, EarlyView.