This study examines the parenting stress and correlations in mothers of young children with autism spectrum disorder (ASD) before 4 years of age. Participants included 121 children with ASD (mean age = 32 months) and their mothers (mean age = 34 years) in the study. The Parenting Stress Index (PSI) was used for measuring the parenting stress in mothers, including child domain, parent domain, and total stress. And, the Child Behavior Checklist (CBCL) was used for measuring behavior problems, including internalizing problems, externalizing problems, and overall problems. In addition, Clancy Behavior Scale (Clancy) with parents’ report and the Autism Diagnostic Observation Schedule (ADOS) with behavior observation were used for assessing autistic symptoms. The results and conclusions of the study showed: 1. Percent of mothers of young children with ASD showed high stress are 30.6%, 25.6% and 29.8% for child domain, parent domain, and total stress, respectively. 2. All of internalizing problems, externalizing problems, overall problems and autistic symptoms significantly correlated with child domain, parent domain, and total stress in mothers of children with ASD. The relationship between autistic symptom measuring by behavior observation and parenting stress is weakness. 3. Both child domain and total stress could be predicted by internalizing problems and externalizing problems, especially for externalizing problems. In addition, autistic symptoms were not predictors. Together with behavioral problem and autistic symptoms explain 47.2%, 23.6% and 40.3% of variance for child domain, parent domain, and total stress, respectively. The findings of the study again supported that 30% mothers of children with ASD showed high parenting stress. The results also showed that behavioral problems are critical predictors for parenting stress in mothers of children with ASD, especially for externalizing problems. The findings of the study suggested that the mothers’ perceptions of child behaviors and characteristics play an important role in parenting stress. This study provided the implications for early intervention in children with ASD.