The present invention relates to a method for controlling a transmission power of a dual standby mode mobile terminal. A method of controlling a transmission power of the invention includes performing a conversation standby service with a first communications network while performing a conversation service with a second communications network, and receiving a first power control level from a base station of the first communications network; comparing a second power control level that corresponds to a power code, which is set for a current output signal power, with the first power control level; and decreasing a current power code when the first power control level is greater than or equal to the second power control level.