Methods and apparatuses are provided for transmitting and receiving system information (SI). A method for receiving SI by a user equipment (UE) in a mobile communication system includes receiving, by the UE, the SI including first partial bits of a system frame number (SFN) without second partial bits of the SFN on a broadcast channel (BCH) at a first subframe of a radio frame, the first partial bits of the SFN having the same value during a predetermined N successive radio frames of a BCH transmission period, where N is a positive integer; and acquiring, by the UE, the second partial bits of the SFN for the radio frame, the second partial bits of the SFN having different values in different radio frames of the predetermined N successive radio frames of the BCH transmission period.