Background <p>Mindfulness-based interventions (MBIs) are increasingly applied to families with autism spectrum disorder (ASD), yet previous research has often examined the effects on individuals with ASD and their parents separately.</p> Objective <p>This systematic review and meta-analysis aimed to examine the effectiveness of MBIs across both groups.</p> Method <p>Six databases were searched from inception to August 2025 for randomized controlled trials (RCTs). Risk of bias was assessed using the Revised Cochrane Risk of Bias tool (RoB 2), with data synthesized via random-effects models and narrative review.</p> Results <p>Among 38 included RCTs (32 for meta-analysis), MBIs significantly alleviated internalizing (<i>g</i> = -0.23, 95%CI [-0.40, -0.06]) and externalizing (<i>g</i> = -0.63, 95%CI [-1.04, -0.21]) behaviors in individuals with ASD, though no significant changes occurred in autism symptoms (<i>g</i> = -0.13, 95%CI [-0.28, 0.03]). For parents, MBIs markedly reduced anxiety (<i>g</i> = -0.53, 95%CI [-0.76, -0.29]), depression (<i>g</i> = -0.61, 95%CI [-0.82, -0.40]), and stress (<i>g</i> = -0.48, 95%CI [-0.73, -0.23]), while significantly enhancing mindfulness (<i>g</i> = 0.68, 95%CI [0.38, 0.98]).</p> Conclusions <p>MBIs hold promise as adjunctive therapies for individuals with ASD and their parents. Moderator analyses revealed that treatment efficacy was significantly influenced by age (individuals with ASD for internalizing behaviors; parents for mindfulness) and geographic region (for parental stress). These findings underscore the critical need for developmentally tailored interventions to optimize outcomes.</p> <p><b>Preregistration</b> This review was preregistered on the Open Science Framework (<a href="https://doi.org/10.17605/OSF.IO/8FVNA">https://doi.org/10.17605/OSF.IO/8FVNA</a>).</p>