Integration of signaling pathways is important for the establishment of the body plan during embryogenesis. However, little is known about how the multiple signals interact to regulate morphogenesis. Here, we show that junb is expressed in the posterior neural plate and the caudal fin during Xenopus embryogenesis and that overexpression of wild-type JunB induces small head phenotypes and ectopic tail-like structures. A mutant form of JunB that lacked GSK3 and MAPK phosphorylation sites showed stronger tail-like structure-inducing activity than wild-type JunB. Moreover, the mutant JunB induced expression of tailbud and neural marker genes, but not somite and chordoneural hinge (CNH) marker genes in ectopic tail-like structures. In ectodermal explants of Xenopus embryos, overexpression of JunB increased the expression of tailbud and posterior marker genes including fgf3, xbra (t) and wnt8. These results indicate that JunB is capable of inducing the ectopic formation of tissues similar to the tailbud, and that the tailbud-inducing activity of JunB is likely to be regulated by FGF and Wnt pathways. Overall, our results suggest that JunB is a regulator of tail organization possibly through integration of several morphogen signaling pathways.