The present invention relates to a wireless communication system. More specifically, the present invention relates to a method and a device for transmitting a contention-based PUSCH in a wireless communication system, the method comprising: configuring a CB grant; configuring a prohibit condition indicating that a data cannot be transmitted using the CB grant; receiving uplink data from an upper layer; checking whether the prohibit condition is met for the uplink data; and transmitting the uplink data using the CB grant if the prohibit condition is not met.