Thyroid volume was proposed as a factor for malignancy in evaluating thyroid nodules. Previous studies have demonstrated the endocrine disrupting effect of polycyclic aromatic hydrocarbons (PAHs), but studies on the association between internal exposure of PAHs and thyroid volume are still scarce. In this work, we evaluated the association of polycyclic aromatic hydrocarbon internal exposure and urinary iodine concentration with thyroid volume in 590 school-age children without thyroid disease in Guangzhou, China. Urinary hydroxylated polycyclic aromatic hydrocarbons (OH-PAHs), urinary iodine concentrations, and thyroid volumes were measured. The mean concentrations of urinary iodine and ΣOH-PAHs were 271.1 μg/L and 3.27 μg/L, respectively, and the mean thyroid volume was 2.4 mL. The associations of urinary iodine and OH-PAH concentrations with thyroid volume were investigated by multivariable linear regression and the Bayesian kernel machine regression models. Urinary ΣOH-PAHs were observed to be significantly positively associated with thyroid volume in multivariable linear regression models. The increase in each unit in the log-transformed concentration of ΣOH-PAHs caused 3.88% change in thyroid volume. The Bayesian kernel machine regression model demonstrated a positive joint effect of increased urinary ΣOH-PAHs on thyroid volume. Moreover, urinary ΣOH-PAHs were statistically significant linked to urinary iodine, and iodine mediated the relationship between urinary OH-PAHs and thyroid volume with the mediated proportions of 15.2%