YM-341619 (AS1617612) is a potent and orally active STAT6 inhibitor with an IC50 of 0.70 nM. YM-341619 inhibits Th2 differentiation in mouse spleen T cells induced by IL-4 (IC50=0.28 nM) without affecting Th1 cell differentiation. YM-341619 is a promising compound for the the research of allergic diseases, such as allergic asthma.