A method for transmitting uplink data using multiple carriers by a User Equipment (UE) in a mobile communication system is provided. The method includes determining a first maximum transmission power indicating a maximum transmission power for each carrier and a second maximum transmission power indicating a maximum transmission power for all carriers based on information for setting transmission power, received from an evolved Node B (eNB), determining a minimum value from among a required transmission power and the first maximum transmission power as an uplink transmission power, for each carrier, scaling the determined uplink transmission powers so that a sum of the uplink transmission powers is less than or equal to the second maximum transmission power, and transmitting the uplink data based on the scaled uplink transmission powers.