Disclosed is a method for handing-off a mobile station receiving packet data over a second channel from a first base station system (BSS) to a second BSS by a base station controller (BSC) in a system in which the mobile station communicates with the first BSS and the second BSS adjacent to the first BSS through a first channel for transmitting a control message, and the mobile station communicates with the first BSS through the second channel for transmitting the packet data. In the method, the mobile station measures receiving strengths of pilot channels transmitted from the first BSS and the second BSS, and transmits the measured receiving strengths to the BSC through the first BSS and the second BSS. The first and second BSSs each calculate available transmission power allocable to the second channel and transmits the calculated available transmission power to the BSC. The BSC calculates a sum of the available transmission power and the measured receiving strength of the pilot channel from the first BSS and a sum of the available transmission power and the measured receiving strength of the pilot channel from the second BSS. The BSC transmits a handoff indication message to the second BSS, when the sum of the available transmission power and the measured receiving strength of the pilot channel from the second BSS is higher than the sum of the available transmission power and the measured receiving strength of the pilot channel from the first BSS.