Provided are a method and an apparatus for transmitting uplink data on the basis of contention in a wireless communication system. Specifically, a terminal receives, from a base station, allocation information for a contention zone in one resource zone. The allocation information includes a configuration field indicating locations and the number of contention zones. The terminal determines whether repetition of uplink data is to be performed, on the basis of downlink channel information. When it is determined that the repetition of uplink data is to be performed, the terminal transmits, to the base station, uplink data through all contention zones indicated by the configuration field. When it is determined that the repetition of uplink data is not to be performed, the terminal transmits, to the base station, uplink data through one contention zone arbitrarily selected from among all the contention zones indicated by the configuration field.