A communication device of handling dual connectivity, comprising: a storage device; and a processing circuit, coupled to the storage device, wherein the storage device stores instructions, and the processing circuit is configured to execute the instructions of: establishing a radio resource control, RRC, connection to a master base station, MBS, via at least one first carrier frequency; receiving a first RRC reconfiguration message from the MBS via the RRC connection, wherein the first RRC reconfiguration message configures the communication device to connect to a secondary base station, SBS, via at least one second carrier frequency configured by the RRC reconfiguration message; determining a first reconfiguration failure according to a first configuration for communicating with the SBS in the first RRC reconfiguration message; transmitting a RRC notification message to the MBS via the RRC connection to indicate the first reconfiguration failure, in response to the first reconfiguration failure; characterised by receiving a second configuration in the first RRC reconfiguration message or in a second RRC reconfiguration message from the MBS via the RRC connection, wherein the second configuration configures a parameter used by the communication device to communicate with the MBS; determining a second reconfiguration failure according to the second configuration; and performing a RRC connection reestablishment procedure with the MBS in response to the second reconfiguration failure. a storage device; and a processing circuit, coupled to the storage device, wherein the storage device stores instructions, and the processing circuit is configured to execute the instructions of: establishing a radio resource control, RRC, connection to a master base station, MBS, via at least one first carrier frequency; receiving a first RRC reconfiguration message from the MBS via the RRC connection, wherein the first RRC reconfiguration message configures the communication device to connect to a secondary base station, SBS, via at least one second carrier frequency configured by the RRC reconfiguration message; determining a first reconfiguration failure according to a first configuration for communicating with the SBS in the first RRC reconfiguration message; transmitting a RRC notification message to the MBS via the RRC connection to indicate the first reconfiguration failure, in response to the first reconfiguration failure; characterised by receiving a second configuration in the first RRC reconfiguration message or in a second RRC reconfiguration message from the MBS via the RRC connection, wherein the second configuration configures a parameter used by the communication device to communicate with the MBS; determining a second reconfiguration failure according to the second configuration; and performing a RRC connection reestablishment procedure with the MBS in response to the second reconfiguration failure. establishing a radio resource control, RRC, connection to a master base station, MBS, via at least one first carrier frequency; receiving a first RRC reconfiguration message from the MBS via the RRC connection, wherein the first RRC reconfiguration message configures the communication device to connect to a secondary base station, SBS, via at least one second carrier frequency configured by the RRC reconfiguration message; determining a first reconfiguration failure according to a first configuration for communicating with the SBS in the first RRC reconfiguration message; transmitting a RRC notification message to the MBS via the RRC connection to indicate the first reconfiguration failure, in response to the first reconfiguration failure; characterised by receiving a second configuration in the first RRC reconfiguration message or in a second RRC reconfiguration message from the MBS via the RRC connection, wherein the second configuration configures a parameter used by the communication device to communicate with the MBS; determining a second reconfiguration failure according to the second configuration; and performing a RRC connection reestablishment procedure with the MBS in response to the second reconfiguration failure.