Objectives: This study investigated parenting stress in South Korean mothers of adolescent children with autism spectrum disorder (ASD) and the variables associated with their parenting stress. Methods: A total of 138 South Korean mothers participated in this study. Descriptive statistics, independent sample t-tests, ANOVA tests, and a stepwise multiple regression analysis were used in this study. Results: The majority of South Korean mothers of adolescent children with ASD in this study showed higher than normal parenting stress. Child’s maladaptive behavior, receipt of early childhood special education, age, and autism severity as well as mother’s receipt of services from mental health professionals were the factors significantly associated with parenting stress. Conclusion: Considering the factors significantly associated with mother’s stress level, interventions focusing on child’s maladaptive behavior and mother’s mental health are important. The interventions aiming to address parenting stress in mothers of adolescent children with ASD may find the findings of this study useful.