Background: Kawasaki disease (KD) is a kind of vasculitis with an unidentified etiology. Cathelicidin (LL-37) may be involved in the development of the KD process; therefore, further research to investigate the molecular mechanism of LL-37 involvement in KD is warranted. Methods: Enzyme-linked immunosorbent assay (ELISA) was used to detect the levels of TNF-α, IL-1β, NLRP3, and LL-37 in the sera of healthy subjects, children with KD, and children with pneumonia. Subsequently, human recombinant LL-37 or/and TLR4-specific inhibitor TAK-242 stimulated HCAECs cells, CCK-8 was used to detect cell proliferation, flow cytometry to detect apoptosis, transmission electron microscopy to observe cytoskeletal changes, Transwell to measure cell migration ability, ELISA to detect inflammatory factor levels, Western blotting to analyze protein levels of TLR4 and NF-κB p-65, and qRT-PCR to determine LL-37, NLRP3 mRNA levels. Results: In this study, we found that the level of LL-37 was highly expressed in the serum of children with KD, and after LL-37 stimulation, apoptosis was significantly increased in HCAECs, and the expression levels of TLR4, NLRP3 and inflammatory factors in cells were significantly enhanced. Intervention with the TLR4-specific inhibitor TAK-242 significantly alleviated the LL-37 effects on cellular inflammation, TLR4, NLRP3 promotion effect. Conclusions: Our data suggest that LL-37 induces an inflammatory response in endothelial cells via TLR4-NF-κB, leading to coronary artery injury in KD, providing a potential target to treat KD.