Background: Little information is available on eosinophil activation and cytokine/chemokine responses in childhood asthma, thus we examined serum eosinophil cationic protein (ECP) and 27 types of cytokines/chemokines in acute exacerbation of asthma (acute asthma) and stable asthma. Methods: We determined peripheral eosinophil count, and the serum levels of ECP and 27 types of cytokines/chemokines (IL-1β, IL-1ra, IL-2, -4, -5, -6, -7, -8, -9, -10, -12, -13, -15 and -17, IFN-γ, IP-10, TNF-α, GM-CSF, G-CSF, MCP-1, MIP-1α and -1β, eotaxin, RANTES, PDGF-bb, FGF basic and VEGF) using a multiplex bead-based assay in 85 acute and 79 stable asthma patients, and 14 controls. We also examined the effects of systemic corticosteroids on these responses in acute asthma. Results: The serum levels of ECP, IL-5, -6, -8 and -10, G-CSF, MCP-1, IL-1ra and IP-10 were significantly elevated in acute compared with stable asthma. Similarly, serum levels of ECP, IL-5 and IP-10 were significantly higher in acute asthma than in controls. Furthermore, in the acute phase, elevated serum levels of ECP, IL-5, IL-6, IL-1ra and IP-10, but not IL-8, IL-10, G-CSF and MCP-1 were significantly reduced after treatments that included systemic corticosteroids. Conclusion: Eosinophil activation could be induced by acute exacerbation of childhood asthma.