A method for receiving system information, a method for transmitting system information by a Node B in a mobile communication system, a user equipment (UE) for receiving system information, and a Node B for transmitting system information by a Node B in a mobile communication system are provided. The method for receiving system information includes receiving system information comprising first partial bits of a system frame number (SFN) on a broadcast channel in a first subframe of a radio frame within a broadcast channel transmission period, the first partial bits having the same value during one broadcast channel transmission period comprising a plurality of radio frames; acquiring second partial bits of the SFN based on decoding the broadcast channel, the second partial bits having different values for different radio frames within the broadcast channel transmission period; and determining the SFN from the first partial bits and the second partial bits.