The present invention relates to a transgenic mouse model for developing enzyme replacement therapy for iduronate-2-sulfatase deficiency syndrome, for example, Hunter syndrome. More specifically, the present invention relates to a transgenic mouse to be used for developing enzyme replacement therapy for iduronate-2-sulfatase, wherein the immune response against injected enzyme, such as, recombinant iduronate-2-sulfatase has been minimized in transgenic mouse model in the course of treating in vivo iduronate-2-sulfatase replacement.