A method and apparatus for controlling a transmission (Tx) power in a mobile communication system based on fractional frequency reuse are provided. In a method of operating a base station (BS) for controlling the Tx power in the mobile communication system, the method includes receiving from neighboring BSs received signal strength indication (RSSI) information for one or more restricted band allocated, calculating backoff values of the Tx power for the restricted bands by using the RSSI information, and determining the Tx power for each restricted band by using a difference between the backoff value of the Tx power for the restricted band and a maximum Tx power. Accordingly, resources can be further effectively used.