p204, an inteferon-inducible protein, is known to play an important role in modulating cell proliferation, cell cycling, and the differentiation of various tissues, including osteoblasts. In order to determine the role of p204 during development in vivo, the teleost zebrafish (Danio rerio), an established vertebrate model for developmental studies, was employed. p204 cDNA was introduced into zebrafish by microinjection, and p204 was ectopically expressed throughout the whole embryo during the early stages of zebrafish embryogenesis, then its expression gradually decreased, mainly in ventrally located cells and retina capsules. Importantly, overexpression of p204 in zebrafish resulted in striking malformations such as bent spine and expanded belly. Furthermore, the expressions of some genes (vent, runx2b, osn) involved in dorsoventral patterning and osteogenesis were significantly upregulated after p204 injection. This study provides not only the in vivo evidences demonstrating the role of p204 during embryonic development, but also new insights into the molecular mechanism by which p204 mediate osteogenesis.