A method and apparatus are provided for transmitting and receiving System Information (SI) in a mobile communication system. The method for receiving the SI by a User Equipment (UE) includes receiving, by the UE, at a fixedly scheduled sub-frame of a predetermined radio frame within a Primary Broadcast CHannel (P-BCH) transmission period, the SI including first partial bits of a System Frame Number (SFN), the first partial bits indicating a repeated value; and acquiring, by the UE, second partial bits of the SFN in the predetermined radio frame by decoding the P-BCH, the second partial bits indicating a different value.