A method is provided for transmitting a physical uplink control channel (PUCCH) in a wireless communication system supporting multiple antennas. The method is performed by a user equipment (UE) having a first antenna port and a second antenna port, and configured for using a multiple-antenna transmit mode for transmission using multiple antennas and a single-antenna transmit mode for transmission using a single antenna. The UE determines that the multiple-antenna transmit mode is to be used for transmitting the PUCCH, and determines a transmit power offset value to be added to a transmit power of the PUCCH depending on a PUCCH format to be used for transmitting the PUCCH using the first and second antenna ports. The UE transmits the PUCCH by using a first PUCCH resource through the first antenna port, and transmits the PUCCH by using a second PUCCH resource through the second antenna port.