The present invention relates to a wireless communication system. More specifically, the present invention relates to a method and a device for performing UL packet measurements in a wireless communication system, the method comprising: receiving configuration information for a plurality of logical channels from an eNB, wherein each of the plurality of logical channels is associated with one of a plurality of logical channel priorities, determining a packet delay for a logical channel priority among the plurality of logical channel priorities by calculating packet delays for PDCP SDUs belonging to a set of logical channels having the logical channel priority, and transmitting a report including the logical channel priority and the packet delay for the logical channel priority to the eNB.