A method for transmitting data in a wireless communication system is provided. The method includes: transmitting first data through a radio resource allocated in a unit of a default transmission time interval (TTI) including at least one sub-frame in a frame including a plurality of sub-frames consisting of a plurality of orthogonal frequency division multiplexing (OFDM) symbols; and transmitting second data through a radio resource allocated in a unit of a modified TTI obtained by changing the number of sub-frames included in the default TTI in the frame.