Context: Physical environment contamination and in particular, air pollution might cause long-term adverse effects in child growth and a higher risk of catching non-communicable diseases later in life.
Objective: This study aimed to overview the human studies on the association of exposure to ambient Particulate Matter (PM) with childhood obesity.
Data Sources: We systematically searched human studies published until March 2018 in PubMed, Scopus, Ovid, ISI Web of Science, Cochrane library, and Google Scholar databases.
Study Selection: All studies that explored the association between PM exposure and childhood obesity were assessed in the present study, and finally, 5 studies were used in the meta-analysis.
Data Extraction: Two independent researchers performed the data extraction procedure and quality assessment of the studies. The papers were qualitatively assessed by STROBE (Strengthening the Reporting of Observational studies in Epidemiology) statement checklist.
Results: The pooled analysis of PM exposure was significantly associated with increased Body Mass Index (BMI) (Fisher’s z-distribution=0.028; 95% CI=0.017, 0.038) using the fixed effects model. We also used a random-effect model because we found a significant high heterogeneity of the included studies concerning the PM (I2=94.4%; P<0.001). PM exposure was associated with increased BMI (Fisher’s z-distribution=0.022; 95% CI=-0.057, 0.102). However, the overall effect size was not significant, and heterogeneity of the included studies was similar to the fixed effect model. 
Discussion: Our findings on the significant association between PM10 exposure and the increased BMI (r=0.034; 95%CI=0.007, 0.061) without heterogeneity (I2=16.6%, P=0.274) (in the studies with PM10) suggest that the PM type might account for the heterogeneity among the studies. 
Conclusion: The findings indicate that exposure to ambient PM10 might have significant effects on childhood obesity.