We recently reported the inhibitory effect of an oral administration of a Sophora flavescens Aiton methanol extract on the development of atopic dermatitis in the NC/Nga model mice. Heme oxygenase (HO)-1 has recently emerged as an important cytoprotective enzyme against oxidative stress and inflammatory responses in many cell types. The aim of this study was to investigate the possible mechanism by which prenylated chalcone (PC, 7,9,2',4'-tetrahydroxy-8-isopentenyl-5-methoxychalcone), a natural product isolated from S. flavescens, inhibited cytokine-induced Th2 chemokine expression in human keratinocytes, HaCaT cells. The level of chemokine expression was measured by reverse transcription-polymerase chain reaction and HO-1 study was performed by Western blot analysis. Interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha)-induced thymus- and activation-regulated chemokine (TARC/CCL17), macrophage-derived chemokine (MDC/CCL22), cutaneous T-cell attracting chemokine (CTACK/CCL27) expression in a dose-dependent manner. Interestingly, PC significantly suppressed IFN-gamma and TNF-alpha-induced TARC/CCL17, MDC/CCL22 and CTACK/CCL27 expression via the induction of heme oxygenase (HO)-1. This suppression was completely restored by HO-1 siRNA, suggesting a direct role of HO-1 for the suppressive effect. Furthermore, exogenous CO, but not other end products of HO-1 activity, also suppressed IFN-gamma and TNF-alpha-induced TARC/CCL17, MDC/CCL22 and CTACK/CCL27 expression. These results demonstrate that prenylated chalcone induces HO-1 expression, which in turn HO-1 and/or CO suppresses Th2 chemokine expressions induced by cytokines in human HaCaT cells.