Objectives <p>This study explored cultural differences in the sources of parenting stress experienced by mothers of children with Autism Spectrum Disorder (ASD) in the U.S. and Japan. The research had two primary objectives: (1) to compare the levels of maternal parenting stress between mothers in the U.S. and Japan across seven dimensions and (2) to investigate relationships between child behavior problems and maternal parenting stress in the U.S. and Japan.</p> Methods <p>A total of 52 U.S. mothers and 51 Japanese mothers, all with children aged 2–12 diagnosed with ASD, completed questionnaires, including the Parenting Stress Index (PSI) and the Child Behavior Checklist (CBCL).</p> Results <p>U.S. and Japanese mothers both reported high levels of parenting stress. However, differences emerged in specific PSI subscales between the two countries. Japanese mothers reported significantly higher stress levels than their U.S. counterparts in Attachment, Depression, and Competence subscales. Furthermore, behavioral problems in children with ASD were significantly associated with maternal parenting stress in both the U.S. and Japan. When considering child age, and maternal physical and emotional health as covariates, we found that maternal emotional health was a confounding factor in the relationship between child behavior problems and maternal parenting stress only for the Japanese sample. We also identified significant group differences in child externalizing behaviors, which have been under-explored in previous studies.</p> Conclusions <p>Cultural distinctions that may influence the experiences of parenting stress among mothers of children with ASD are discussed while also highlighting the presence of high stress levels in both countries.</p>