Left-right(L-R)patterning is essential for proper organ morphogenesis and function in developing vertebrate embryos.In zebrafish,Kupffer’s vesicle(KV),a central organ for establishing L-R asymmetry,is derived from a group of superficial cells in the organizer region of the gastrula named the dorsal forerunner cells(DFCs).REDD1/Redd1 is an important regulator in response to various stress conditions and regulates diverse signaling pathways.However,little is known about the function of REDD1/Redd1 in determination of L-R asymmetry.Here,we identified that Redd1 is required for L-R asymmetry in zebrafish embryos.Zebrafish redd1 mRNA expression was detected in DFCs or KV progenitor cells and later in the KV at early somitogenesis stages.Morpholino-mediated knockdown of redd1 in the whole embryo or specifically in DFCs perturbed asymmetric gene expression in the lateral plate mesoderm,impaired the formation of the midline molecular barrier,and interrupted the L-R asymmetry of the heart.Knockdown of redd1 in DFCs reduced KV size and impaired ciliogenesis with down-regulation of sox17 and foxj1a.Our results suggest a new and essential role for Redd1 in the determination of KV formation and regulation of L-R asymmetry in zebrafish.