Adult separation anxiety disorder (ASAD) is classified under anxiety disorders in "Diagnostic and Statistical Manual of Mental Disorders" (5th ed.; DSM-5). However, the reasons for ASAD are uncertain. The relationship between ASAD and childhood experiences is one of the frequently debated issues. The purpose of this study was to develop a model that would examine the mediating roles of insecure attachment dimensions--avoidance and anxiety--in the relationship between adults' retrospective perceptions of parental acceptance-rejection in childhood and separation anxiety. A total of 1,534 participants completed Parental Acceptance-Rejection Questionnaire, Experiences in Close Relationships--Revised, Adult Separation Anxiety Questionnaire, and personal information form. The results of the structural equation model indicated that insecure attachment dimensions--avoidance and anxiety variables--fully mediated the relationship between perceived parental acceptance-rejection and separation anxiety. These findings shed new light on the relationship between adults' retrospective perceptions of childhood experiences and adult separation anxiety.