The present invention relates to a wireless communication system. More specifically, the present invention relates to a method and a device for cancelling BSR or SR in dual connectivity, the method comprising: receiving an UL data from an upper layer, triggering a BSR (or SR) for a first eNB due to the UL data, transmitting, to a second eNB, at least a part of the UL data using an UL grant received from the second eNB, and cancelling the triggered BSR (or pending SR) when an amount of data available for transmission to be transmitted to the first eNB changes to zero due to the transmission of the at least a part of the UL data, even if an UL grant in response to the triggered BSR (or pending SR) is not received from the first eNB.