Cell growth and proliferation are essential for the normal development. Myc is well-known as a proliferation-inducing gene. Due to its intrinsic ability of Myc to induce cell proliferation, it is not surprising that Myc proteins play important roles during development. We report that Myc in early zebrafish embryos is turned over quickly, with a half life as short as 10 min. Overexpression of Myc in zebrafish embryos resulted in a phenotype with shorter body axis and twisted tail, while overexpression of a truncated Myc with deletion of Myc-box2 domain resulted in the same phenotype, indicating that the developing role of Myc is independent of Myc-box2, but more likely dependent on the C-terminal bHLHZip domain to compete with other Max interacting proteins for Max. Overexpression of Myc disrupted multiple structures including somites, hindbrain and notochord, showing possible deficiency in convergence & extension movements.