Objectives <p>Grounded in the family model of emotion regulation development, this longitudinal study examined how mindful parenting influences emotion regulation in autistic children and adolescents, as well as its subsequent effects on their internalizing, externalizing, and prosocial behaviors.</p> Method <p>Using a three-wave longitudinal design with annual assessments (i.e., T1, T2, and T3), we collected questionnaire data from 363 parents (68 fathers and 295 mothers) of autistic children and adolescents (304 males and 59 females, aged 5–21&#xa0;years) in Hong Kong. Parents reported on their mindful parenting practices and their autistic children’s and adolescents’ emotion regulation and behavioral adjustment. Path analyses and bootstrapping were used to examine variable relationships.</p> Results <p>Path analyses revealed that mindful parenting at T1 was associated with improved emotion regulation in autistic children and adolescents at T2 (<i>p</i> = 0.002), which subsequently led to reduced internalizing (<i>p</i> = 0.001) and externalizing (<i>p</i> &lt; 0.001) problems and increased prosocial behavior (<i>p</i> = 0.02) in these children and adolescents at T3. Bootstrapping further showed that mindful parenting at T1 indirectly contributed to the improved behavioral outcomes at T3 through its positive impact on emotion regulation at T2.</p> Conclusions <p>Our findings indicate that mindful parenting facilitates the development of better emotion regulation skills in autistic children and adolescents, leading to reduced behavioral problems and enhanced prosocial engagement. These results suggest that clinical practitioners should develop targeted interventions to strengthen parents’ mindful parenting practices, which may ultimately improve emotional and behavioral outcomes for their autistic children and adolescents.</p> Preregistration <p>This study is not preregistered.</p>