Since the host-cell range of a specific virus is predetermined by its ability to recognize specific receptors, the similarities between the receptors of its primary reservoir host cell and the potential human host cell play a major role in determining the likelihood of viral zoonosis. Here, we analysed zoonotic and non-zoonotic RNA viruses along with their cellular receptors in human and (non-human) primary reservoir species to extract the receptor characteristics common to zoonosis. Viruses not previously reported to infect humans were classified as non-zoonotic viruses. We excluded all viruses known to utilize co-receptors; i.e., only virus-receptor interactions occurring through virus tropism and pathogenesis were considered [5, 21] . The receptors and viruses examined in this study are listed in Table 1 . We hypothesized that the major barrier to the transmission of viruses between species is the difference in cellular receptor sequences. In other words, the specific amino acid sequence of the receptor should be the major determinant of the ability of the viral envelope protein to attach to the cell. Ordinary sequence alignment protocol tells us overall sequence similarity which we thought useful but insufficient because most receptors are membrane proteins and membrane proteins consist of distinctive hydrophobic and hydrophilic parts. Therefore, we analysed host-cell receptor sequences for their hydrophobicity/hydrophilicity characteristics. We then analysed these properties for similarities among receptors of different species to predict the likelihood of transmission across species, including humans. To our best knowledge, this study is the first attempt to predict zoonosis through a simple analysis of receptor sequence similarities and differences. This method may be useful in predicting the zoonotic potential of newly discovered viral strains.