Intravenous immunoglobulin (IVIG) resistance leads to serious complications in Kawasaki disease (KD) with no effective treatment. This study aimed to investigate the effects of pentraxin 3 (PTX3) on human coronary artery endothelial cells (HCAECs). PTX3 levels were measured using quantitative real-time PCR (qRT-PCR), enzyme-linked immunosorbent assay, and western blotting. Cell viability was detected using the MTT assay. Biological functions were analyzed using CCK-8, EdU, flow cytometry, TUNEL, and qRT-PCR. The levels of factors of the NF-κB pathway were examined using western blotting. The results demonstrated that PTX3 expression was highest in patients and HCAECs with IVIG-resistance. Knockdown of PTX3 promoted proliferation and suppressed apoptosis and inflammation of IVIG-resistant HCAECs, whereas PTX3 overexpression produced the opposite results. Moreover, PTX3 activated the NF-κB pathway in IVIG-resistant HCAECs. A rescue study showed that PTX3 modulated biological behaviors by regulating the NF-κB pathway. Overall, our findings demonstrate that PTX3 promotes IVIG resistance-induced endothelial injury by activating the NF-κB pathway, suggesting that PTX3 may become a novel therapeutic target for patients with IVIG-resistant KD.