The present invention relates to a broadband wireless access system, and more particularly, to a method and an apparatus for acquiring system information in a mobile communication system in which a legacy system and an advanced system coexist. A method of receiving system information on a peripheral base station in a mobile communication system includes receiving a second message containing time information for receiving, through a second region of a serving base station, a first message broadcasted through a first region of the serving base station and receiving the first message through the first region of the serving base station using the time information, the first message containing system information on neighbor legacy base stations and/or on the first region of neighbor advanced base stations which operate in a mixed mode.