A method for transmitting sidelink data by a User Equipment (UE) in a wireless communication system includes determining whether resource pool information for selecting a sidelink grant is configured by a base station; determining whether more sidelink data is available in a Sidelink Traffic Channel (STCH) than can be transmitted in a current Sidelink Control (SC) period; selecting resources for the sidelink grant from the resource pool information based on the resource pool information for selecting the sidelink grant being configured by the base station, and more sidelink data being available in the STCH than can be transmitted in the current SC period; selecting resources for the sidelink data based on the resources for the sidelink grant; and transmitting the sidelink data to another UE through the resources for the sidelink data. Further, the sidelink grant is for a next SC period after the current SC period.