Background: This study examined the severity of parenting stress and depressive symptoms in Taiwanese mothers of young children with autism spectrum disorder (ASD) compared to mothers of young children with developmental delay (DD). The associations between parenting stress, depressive symptoms, and children's behavioural problems were also tested. Methods: The study sample included 51 young children with ASD (mean age = 31 months), 51 young children with DD (mean age = 30 months) and their mothers. Results: The results confirmed that mothers of young children with ASD experienced higher levels of parenting stress and depressive symptoms than mothers of young children with DD. In addition, children's behavioural problems were robust predictors of parenting stress and depressive symptoms in mothers of young children with ASD, but not in mothers of young children with DD. Conclusion: The findings indicated that one of the critical goals in early intervention for young children with ASD and their families is to reduce children's behavioural problems.