To find a new use as a therapeutic agent for dog diseases because the dog IFN-γ is considered to be especially effective as a therapeutic agent for a great number of known dog diseases such as a great number of tumors, e.g. mammary gland tumor, a great number of viral diseases such as parbovirus infectious diseases, distemper virus infectious diseases, etc., and a great number of skin diseases, etc., if IFN-γ is mass produced and is readily obtainable.

A high-purity protein having interferon-γ activity is produced by using a metal chelate carrier, an ion exchange carrier and a coloring matter carrier.