A method of allocating control information in a wireless communication system is provided. The method includes: allocating essential control information of a first system to a first sub-frame in a frame including a plurality of sub-frames each of which comprises a plurality of orthogonal frequency-division multiplexing (OFDM) symbols; and allocating essential control information of a second system to an nth sub-frame in a fixed position from the first sub-frame (where n is an integer satisfying n>1). Accordingly, in a frame supporting heterogeneous systems, essential control information can be fixedly allocated to a specific position while maintaining the number of system switching points, at which switching occurs between the systems, to one even if a radio resource allocation amount changes between the systems, and thus the essential control information that must be received by all user equipments can be effectively provided without the increase of overhead.