A method for compensating transmission power deviations of channels in a mobile phone using adjustment channels, which is capable of minimizing transmission power deviations of channels while efficiently compensating for those transmission power deviations. The adjustment channels are selected from channels for mobile phone services while including a reference one of available channels allocated to the mobile phone from the channels for mobile phone services, the number of the adjustment channels being less than the number of the allocated available channels. Respective transmission automatic gain control (AGC) level values for the adjustment channels are stored in the non-volatile memory of the mobile phone. The method involves an offset value processing procedure for reading out the transmission AGC level values from the non-volatile memory, and deriving offset values corresponding to respective differences between the transmission AGC level value of the reference channel and respective transmission AGC level values of the remaining adjustment channels, and a compensation value processing procedure for deriving a compensation value for a currently available one of the allocated available channels, based on offset values of upper and lower limit adjustment channels, located above and below the currently available channel, respectively, a channel span between the currently available channel and the lower limit adjustment channel, and a channel span between the upper and lower limit adjustment channels.