Kawasaki disease (KD) is a systemic vasculitis of unknown etiology. The laboratory findings before and after intravenous immunoglobulin (IVIG) in KD have been discussed, but the characteristics of IVIG therapy still are unclear. This study aimed to compare laboratory data from patients with KD and enterovirus (EV) infection to evaluate the differences after IVIG therapy. The study enrolled 171 KD patients and 38 EV patients treated with a single dose of IVIG from 2003 to 2010. Laboratory data including total white blood cell counts (WBC) and hemoglobin (Hb), platelet, segment, lymphocyte, eosinophil, and monocyte levels were analyzed. Compared with the KD patients, the EV patients had higher Hb, lymphocyte, and monocyte levels and lower eosinophil levels before IVIG treatment (p < 0.05). After IVIG treatment, the KD patients had lower Hb and segment levels but higher platelet, lymphocyte, and eosinophil levels than the EV patients (p < 0.05). In the KD patients, the platelet, eosinophil, and monocyte levels increased after IVIG treatment, whereas Hb, WBC, and segment levels decreased significantly (p < 0.001). In the EV patients, eosinophil levels increased after IVIG treatment, whereas WBC and Hb levels decreased significantly (p < 0.05). The study results provide evidence that eosinophilia may be related to IVIG therapy in KD and EV patients. The KD patients had higher eosinophil levels both before and after IVIG therapy than the EV patients, which may have been due to the inflammatory mechanism of KD. The KD patients had higher platelet levels than the EV patients, suggesting that platelets are involved in the inflammatory response to KD.