Objective <p>Coronary artery lesions (CALs) are a specified feature of Kawasaki disease (KD), occurring in the second week of onset. The current study was to unravel the correlation between peripheral blood T helper 17/regulatory T (Th17/Treg) immune imbalance and CALs in children with KD.</p> Methods <p>In this cross-sectional study, 198 KD children were evaluated for their CALs as per the coronary arterial internal diameter, and allocated into the CAL and non-CAL groups, with their general baseline data and laboratory parameters collected. Peripheral blood Th17 and Treg were measured by flow cytometry, with Th17/Treg calculated. The correlations of peripheral blood Th17/Treg with the coronary arterial internal diameter and interleukin (IL)-6, the diagnostic value of neutrophil-lymphocyte ratio (NLR) and peripheral blood Th17/Treg for CALs, and the independent risk factors for CALs in KD children were analyzed by the Spearman’s, receiver operating characteristic curve and multivariate logistic regression analyses, respectively.</p> Results <p>NLR, C-reactive protein, IL-6, and Th17/Treg levels and percentage of anemia were higher in CAL children than in those with non-CAL (all <i>P</i> &lt; 0.05). Peripheral blood Th17/Treg positively correlated with the coronary arterial internal diameter and IL-6 in CAL-KD children (all <i>P</i> &lt; 0.001). Peripheral blood Th17/Treg &gt; 71.56% had high diagnostic value for CALs in KD children (area under the curve: 0.856). Peripheral blood Th17/Treg was an independent risk factor for CALs in KD children (<i>P</i> &lt; 0.05).</p> Conclusion <p>Peripheral blood Th17/Treg &gt; 71.56% is effective in diagnosing CALs in KD children. Th17/Treg is an independent risk factor for CALs.</p>