The present invention relates to a long-acting interferon beta formulation having improved in vivo duration and stability, comprising an interferon beta conjugate that is prepared by covalently linking interferon beta with an immunoglobulin Fc region via a non-peptidyl polymer, and a preparation method thereof. The long-acting interferon beta formulation of the present invention maintains in vivo activity of interferon beta at a relatively high level and remarkably increases the serum half-life thereof, thereby being used for various diseases, for which interferon is efficacious.
