To evaluate the antiallergic effect of fermented Ixeris sonchifolia (IS, family Compositae), we prepared IS kimchi, isolated lactic acid bacteria (LAB) from it, fermented IS with these LAB, and investigated their antiallergic effects. IS kimchi inhibited the passive cutaneous anaphylaxis (PCA) reaction induced by an IgE-antigen complex as well as the scratching behavior induced by compound 48/80 or histamine more potently than IS. When IS was fermented with LAB isolated from IS kimchi, its antiallergic effects was also increased. Of LAB used for fermentation, Lactobacillus brevis more potently increased the antiallergic effects. Its main constituents, chlorogenic acid and luteolin, potently inhibited the PCA reaction induced by the IgE-antigen complex as well as the pruritis induced by compound 48/80 or histamine. These constituents inhibited the expression of pro inflammatory and allergic cytokines, TNF-$alpha$. and IL-4, and transcription factor NF-${kappa}B$ activation induced by the IgE-antigen complex in RBL-2H3 cells, as well as the degranulation of RBL-2H3 cells induced by the IgE-antigen complex. Luteolin more potently inhibited these allergic reactions than chlorogenic acid. These findings suggest that the antiallergic effect of IS can be increased by LAB fermentation, and the fermented IS might improve allergic reactions such as pruritus, anaphylaxis, and inflammation.