The present invention relates to a wireless communication system. More specifically, the present invention relates to a method and a device for selecting prose destinations or SL grants in a D2D communication system, the method comprising: receiving or selecting N numbers of SL grants used for a next SC period; selecting ProSe destinations in decreasing order of priority of ProSe destination so that selected numbers of ProSe destinations are equal to N, wherein a priority of ProSe destination is set to priority of a SL logical channel with a highest priority among all SL logical channels associated with the ProSe destination; and transmitting SL data of the selected ProSe destinations using the N numbers of SL grants in the next SC period, wherein SL data of each of the selected ProSe destinations is transmitted using a corresponding SL grant among the N numbers of SL grants.