Vitelline membrane outer layer protein 1 or VMO1 (18 kDa) is one of the most abundant proteins in the outer layer of the chicken egg vitelline membrane, a fibrous protein layer surrounding the yolk. Its 3D structure consists of three homologous beta sheets forming a so-called beta-prism fold. Although this fold has been found in plant jacalin-like lectins, the biological function of VMO1 remains unknown to date. In a gene expression study performed on various reproductive and non-reproductive hen tissues, we observed that VMO1 gene is highly expressed in the oviduct (egg-forming organ), while no or very low expression is detected in the other tissues analyzed. Chicken VMO1 was purified from a soluble vitelline membrane extract and further characterized by mass spectrometry. As expected, purified mature VMO1 is composed of 163 amino acids, with an observed average mass of 17,969.4 Da (theoretical mass: 17,970.29 Da). Multiple sequence alignment of various avian VMO1 sequences revealed that VMO1 is strongly conserved in birds. Interestingly, homologues of chicken VMO1 are also identified in both oviparous and viviparous vertebrate animals, as well as in invertebrate organisms. Three highly similar sequence motifs corresponding to three adjacent loop regions in the 3D structure of chicken VMO1, and possibly forming a ligand binding site, are highly conserved in these non-avian sequences. Altogether, this preliminary work suggests that chicken VMO1 has a role in avian reproduction and highlights the possible role of specific loop regions in the biological activity of VMO1.