Coiled-coil domain containing 134 (CCDC134), a characterized secreted protein, may serve as an immune cytokine and illustrates its potent antitumor effects by augmenting CD8+ T-cell-mediated immunity. Additionally, CCDC134 may also act as a novel regulator of human alteration/deficiency in activation 2a, and be involved in the p300-CBP-associated factor complex and affect its acetyltransferase activity. To clarify the biological and pathological function of CCDC134, the present study generated a viable and fertile Ccdc134fl/fl mouse strain that allowed temporal and spatial control of gene ablation. Ccdc134-/- embryos generated by crossing of Ccdc134fl/fl mice with human β-actin-Cre or zona pellucida 3-Cre transgenic mice were embryonic lethal from embryonic day (E)12.5 to birth. Ccdc134 loss was associated with severe hemorrhages in the brain ventricular space and neural tube, pale and abnormal livers, cardiac hypertrophy and placental distress. Furthermore, it was demonstrated that a fraction of E13.5 fetal livers and brains exhibited reduced cell proliferation and vascular endothelial cell defects. CCDC134 also exhibited a dynamic and specific expression pattern during embryo development. The present results suggest that Ccdc134 may have specific biological functions in regulating mouse embryonic development.