Purpose: This study examined the effects of using a short-term DIRFloortime therapy approach to treat the child of an immigrant family in South Korea, who had been diagnosed with autism spectrum disorder(ASD) and had experienced adverse childhood experiences(ACEs). Method: A case study, in which the DIRFloortime therapy approach was tailored to meet the family and the child’s needs, was used to delineate the efficacy of the therapy approach. Results: Results showed that the child improved in self-regulation, showed more engagement in relationships with others, including his mother and therapist, developed a sense of self, and decreased externalized negative behaviors. Conclusion: Treatment approaches often fail to adequately focus on autistic children’s mental health history and its impact. This case study sheds light on the autistic child’s history of ACEs and how DIRFloortime was used to reduce the child’s negative externalized behaviors.