The present invention relates to a wireless communication system. More specifically, the present invention relates to a method and a device for handling of data transmission and reception for SeNB related bearer release in a dual connectivity system, the method comprising: receiving, from a Master eNB (MeNB), a 1st message for requesting to release a SCG (Secondary Cell Group) bearer or a SCG part of a split bearer configured in the SeNB; releasing downlink part of the SCG bearer or the SCG part of the split bearer configured in the SeNB; receiving, from the MeNB, a 2nd message for indicating that a UE has released the SCG bearer or the SCG part of the split bearer configured in the SeNB; and releasing uplink part of the SCG bearer or the SCG part of the split bearer configured in the SeNB.