A user equipment, UE, for handling a signaling radio bearer, SRB, of a narrowband internet of things, NB-IoT, communication, comprising: a storage device for storing instructions; a processing circuit, coupled to the storage device, wherein the storage device stores, and the processing circuit is configured to execute, the instructions of: receiving a RRC connection reconfiguration message from a network, when the UE is in RRC_CONNECTED mode, wherein the RRC connection reconfiguration message indicates a full configuration and comprises a SRB configuration; checking whether there is any srb-Identity value comprised in the SRB configuration or not, after receiving the RRC connection reconfiguration message; applying a default SRB configuration, a default RLC configuration and a default logical channel configuration for at least one SRB according to at least one srb-Identity value in the SRB configuration, when there is the at least one srb-Identity value comprised in the SRB configuration; and applying the default SRB configuration, the default RLC configuration and the default logical channel configuration for SRB Type 1, SRB1, when there is no srb-Identity value comprised in the SRB configuration; and wherein the UE supports at least one NB-loT capability; wherein the RRC connection reconfiguration message is a RRCConnectionReconfiguration message or a RRCConnectionReconfiguration-NB message; and wherein the SRB configuration is a srb-ToAddModList or a srb-ToAddModList-NB; and applying the default SRB configuration, the default RLC configuration and the default logical channel configuration for all SRBs supported by the UE. a storage device for storing instructions; a processing circuit, coupled to the storage device, wherein the storage device stores, and the processing circuit is configured to execute, the instructions of: receiving a RRC connection reconfiguration message from a network, when the UE is in RRC_CONNECTED mode, wherein the RRC connection reconfiguration message indicates a full configuration and comprises a SRB configuration; checking whether there is any srb-Identity value comprised in the SRB configuration or not, after receiving the RRC connection reconfiguration message; applying a default SRB configuration, a default RLC configuration and a default logical channel configuration for at least one SRB according to at least one srb-Identity value in the SRB configuration, when there is the at least one srb-Identity value comprised in the SRB configuration; and applying the default SRB configuration, the default RLC configuration and the default logical channel configuration for SRB Type 1, SRB1, when there is no srb-Identity value comprised in the SRB configuration; and wherein the UE supports at least one NB-loT capability; wherein the RRC connection reconfiguration message is a RRCConnectionReconfiguration message or a RRCConnectionReconfiguration-NB message; and wherein the SRB configuration is a srb-ToAddModList or a srb-ToAddModList-NB; and applying the default SRB configuration, the default RLC configuration and the default logical channel configuration for all SRBs supported by the UE. receiving a RRC connection reconfiguration message from a network, when the UE is in RRC_CONNECTED mode, wherein the RRC connection reconfiguration message indicates a full configuration and comprises a SRB configuration; checking whether there is any srb-Identity value comprised in the SRB configuration or not, after receiving the RRC connection reconfiguration message; applying a default SRB configuration, a default RLC configuration and a default logical channel configuration for at least one SRB according to at least one srb-Identity value in the SRB configuration, when there is the at least one srb-Identity value comprised in the SRB configuration; and applying the default SRB configuration, the default RLC configuration and the default logical channel configuration for SRB Type 1, SRB1, when there is no srb-Identity value comprised in the SRB configuration; and wherein the UE supports at least one NB-loT capability; wherein the RRC connection reconfiguration message is a RRCConnectionReconfiguration message or a RRCConnectionReconfiguration-NB message; and wherein the SRB configuration is a srb-ToAddModList or a srb-ToAddModList-NB; and applying the default SRB configuration, the default RLC configuration and the default logical channel configuration for all SRBs supported by the UE.