Background <p>The prevalence of autism spectrum disorder (ASD) has increased substantially in recent years, yet evidence regarding the effects of exercise on core ASD symptoms remains inconclusive. Therefore, this study aimed to systematically evaluate the intervention and maintenance effects of exercise on core symptoms in children with ASD using a three-level meta-analysis, and to explore potential moderators and dose-response relationships.</p> Methods <p>Randomized controlled trials (RCTs) examining the effects of exercise interventions on core symptoms in children with ASD were identified through searches of six databases: China National Knowledge Infrastructure (CNKI), PubMed, Web of Science, the Cochrane Library, Embase, and Scopus. Risk of bias was assessed using the Cochrane Risk of Bias tool 2.0 (RoB 2.0). Effect sizes were synthesized using the metafor package in R, with additional analyses including moderator analyses, dose-response modeling, sensitivity analyses, and assessments of publication bias. The certainty of evidence was evaluated using GRADEpro.</p> Results <p>A total of 20 studies involving 874 children with ASD were included. Moderate-certainty evidence indicated that exercise was associated with a statistically significant improvement in core ASD symptoms (Hedges’ g (g) = -0.53, 95% confidence interval (CI) -0.76 to -0.30, <i>P</i> &lt; 0.001; 95% prediction interval (PI) -1.35 to 0.29). Low-certainty evidence suggested that the maintenance effects of exercise were not statistically significant (g = -0.46, 95% CI -0.97 to 0.06, <i>P</i> = 0.074; 95% PI -0.97 to 0.06). Age (F(1, 83) = 9.23, <i>P</i> = 0.003) and type of control condition (F(2, 82) = 4.80, <i>P</i> = 0.011) were identified as significant moderators of intervention effects, whereas core symptom domain, exercise modality, session duration, intervention duration, and exercise frequency were not significant moderators (<i>P</i> &gt; 0.050). Furthermore, neither linear nor nonlinear spline models revealed significant associations between total exercise volume or weekly exercise duration and intervention effects (<i>P</i> &gt; 0.050).</p> Conclusions <p>Based on the current evidence, exercise interventions may be associated with improvement in core symptoms in children with ASD, with effects moderated by age and the type of control condition. However, these findings should be interpreted cautiously in light of the prediction interval crossing zero, the methodological limitations of the included studies, and the limited evidence regarding maintenance effects. No significant dose-response relationship was observed for total or weekly exercise duration. Overall, exercise may be considered a promising supportive approach within the broader range of interventions for ASD, rather than a stand-alone or definitively established strategy. Its long-term effects and optimal exercise prescriptions still require confirmation through high-quality studies.</p> Clinical trial number <p>Not applicable.</p>