Disclosed are a method and an apparatus for transmitting uplink data by means of multiple serving cells. A method for a terminal for transmitting uplink data by means of multiple serving cells may comprise the steps of: the terminal receiving a first timing advance command (TAC) for a first serving cell and a second TAC for a second serving cell; and determining whether the terminal transmits uplink data by means of the second serving cell on the basis of whether the timing difference is below the threshold value, wherein the timing difference is acquired on the basis of the first TAC and the second TAC, and the first serving cell can be a cell configured so that an uplink can be always transmitted regardless of the timing difference.