A method is provided in which the recognition specificity of a virus for a receptor sugar chain can be easily determined with a simple instrument or apparatus. This method for determining the recognition specificity of a virus for a receptor sugar chain or for determining the change in a host infected in accordance with the mutation of virus includes the steps of bringing a sample of the virus into contact with a support having a polymer with sialo-oligosaccharide immobilized on the surface thereof; and assaying the degree of binding therein to determine the recognition specificity of the virus for the receptor sugar chain and to determine the change in a host range. The method is suitable for the surveillance of a virus.