Objective During zebrafish embryo gastrulation, the embryonic body plan is established by coordinated movements, including epiboly, involution, and convergence and extension (CE) movements. The aim of this study was to examine the expression patterns and the developmental functions of isthmin 1 ( ism1) during zebrafish gastrulation. Methods First, the expression of ism1 was examined using whole mount in situ hybridization during zebrafish embryonic development. Next, antisense morpholino oligonucleotide against ism1 and ism1 mRNA were injected into zebrafish embryos, respectively, to investigate its role in CE movements. Results ism1 is an early zygotic gene that is expressed in the dorsal side at 30% epiboly stage and in the blastoderm margin with the highest level in the dorsal organizer at shield stage as revealed by whole-mount in situ hybridization experiments. Compared with the wild-type embryos, either gain- or loss-of-function of ism1 leads to severe defects of CE movements. Conclusions Ism1 plays an essential role in CE movements during zebrafish embryo gastrulation.