UNLABELLED: Coronary artery lesions (CAL) are the most common complication of Kawasaki disease (KD). Chinese guidelines recommend aspirin at 30-50 mg/kg/day during the acute phase, yet whether the dose within this range affects coronary outcome remains unclear. We retrospectively analyzed 997 children with complete or incomplete KD who received IVIG plus aspirin at two tertiary hospitals in Sichuan, China, from January 2017 to December 2025. Low-dose aspirin (30 to < 40 mg/kg/day; n = 630) was compared with high-dose (40 to 50 mg/kg/day; n = 367). Confounders were selected by intersecting a directed acyclic graph (Supplementary Fig. S1) with univariate screening at P < 0.10, yielding a final multivariable model of 7 predictors (136 CAL events; events-per-variable ratio of 19.4). Linearity of the continuous covariates and the absence of multicollinearity were verified (Supplementary Tables S1-S2). The dose-response relation was examined with restricted cubic splines, and inverse probability of treatment weighting (IPTW) was added as a sensitivity analysis. CAL at 4 weeks occurred in 13.5% of the low-dose group and 14.7% of the high-dose group (P = 0.658), with an adjusted OR of 0.94 (95% CI 0.64-1.38; P = 0.752). IVIG non-response was similar (4.1% vs 3.8%; P = 0.940), whereas aspirin-related adverse drug reactions were twice as frequent with high-dose aspirin (3.0% vs 6.3%; P = 0.021). The spline showed no significant linear (P = 0.253) or non-linear (P = 0.547) dose-response trend. IPTW yielded an OR of 0.95 (95% CI 0.65-1.38), and the doubly robust estimate was 0.95 (95% CI 0.65-1.40). CONCLUSIONS: Within the guideline-recommended 30-50 mg/kg/day window, no significant differences were detected between low- and high-dose aspirin in coronary or IVIG non-response outcomes, while the lower dose halved adverse drug reactions. Although equivalence cannot be formally demonstrated in an observational study, these data suggest that 30 to < 40 mg/kg/day may be the preferable choice during the acute phase of KD in Chinese children. WHAT IS KNOWN: • Chinese guidelines recommend aspirin at 30-50 mg/kg/day during the acute phase of KD, yet comparative coronary outcome data within this dose range remain limited. WHAT IS NEW: • In a two-center cohort of 997 children, low-dose (30 to < 40 mg/kg/day) and high-dose (40 to 50 mg/kg/day) aspirin produced similar coronary artery lesion rates and IVIG non-response rates, whereas the lower dose halved the rate of adverse drug reactions.