Objective: To elucidate the physiological functions of Coenzyme Q biosynthesis protein 4 homolog (Coq4) in mammals using Coq4 knockout mice. Methods: Coq4 global knockout mouse model was established, and the different genotypes of mice were detected by genomic PCR. The phenotypes and growth and reproduction of wild-type, heterozygous and global knockout mice were observed and recorded; the morphology and structure of embryonic and placental tissues of wild-type and knockout mice were studied by anatomic and histological analyses, and by immunofluorescence assay. Results: Coq4 knockout mice died by E10.5 and exhibited impaired gastrulation on E7.5. Morphological analysis showed that embryonic development of Coq4 knockout mice was severely retarded compared with the wild type, and the placental structure was obviously abnormal. Immunofluorescence analysis revealed that trophoblast cell invasion was diminished. Conclusion: 1. Coq4 is essential for embryonic development; 2. The formation of placenta and gastrula is impeded in Coq4 knockout mice.