Respiratory syncytial virus (RSV) has been reported to use CX3CR1 in vitro as a receptor on cultured primary human airway epithelial cultures. To evaluate CX3CR1 as the receptor for RSV in vivo , we used the cotton rat animal model because of its high permissiveness for RSV infection. Sequencing the cotton rat CX3CR1 gene revealed 91% amino acid similarity to human CX3CR1. Previous work found that RSV binds to CX3CR1 via its attachment glycoprotein (G protein) to infect primary human airway cultures. To determine whether CX3CR1-G protein interaction is necessary for RSV infection, recombinant RSVs containing mutations in the CX3CR1 binding site of the G protein were tested in cotton rats. In contrast to wildtype virus, viral mutants did not grow in the lungs of cotton rats. When RSV was incubated with an antibody blocking the CX3CR1 binding site of G protein and subsequently inoculated intranasally into cotton rats, no virus was found in the lungs four days post-infection. In contrast, growth of RSV was not affected after pre-incubation with heparan sulfate (the receptor for RSV on immortalized cell lines). A reduction in CX3CR1 expression in the cotton rat lung through the use of peptide-conjugated morpholino oligomers led to a 10-fold reduction in RSV titers at day four post-infection. In summary, these results indicate that CX3CR1 functions as a receptor for RSV in cotton rats, and in combination with data from human airway epithelial cell cultures, strongly suggest that CX3CR1 is a primary receptor for naturally acquired RSV infection. Importance The knowledge about a virus receptor is useful to better understand the uptake of a virus into a cell and potentially develop antivirals either directed against the receptor molecule on the cell or the receptor-binding protein of the virus. Amongst a number of potential receptor proteins, human CX3CR1 has been demonstrated to act as receptor for respiratory syncytial virus (RSV) on human epithelial cells in tissue culture. Here we report that the cotton rat CX3CR1 which is similar to the human molecule acts as receptor in vivo. This study strengthens the argument that CX3CR1 is a receptor molecule for RSV.