A communication device for handling data transmission/reception for dual connectivity, comprising: a storage unit for storing instructions; and a processing circuit, coupled to the storage unit, wherein the storage unit stores, and the processing means is configured to execute, the instructions: connecting to a first base station, BS, and a second BS; communicating a first data with the first BS, wherein the first data is encrypted according to a first security key, which is generated according to a first parent key; communicating a second data with the second BS, wherein the second data is encrypted according to a second security key which is generated according to a second parent key; receiving a message from the first BS, wherein the message configures a handover to a third BS and a connection change to a fourth BS; the instructions are further characterised by: updating the first parent key to a first updated parent key and updating the second parent key to a second updated parent key based on the first updated parent key in response to the message; updating the first security key to a first updated security key based on the first updated parent key and updating the second security key to a second updated security key based on the second updated parent key, in response to the message; communicating a third data with the third BS, wherein the third data is encrypted according to the first updated security key; and communicating a fourth data with the fourth BS, wherein the fourth data is encrypted according to the second updated security key. a storage unit for storing instructions; and a processing circuit, coupled to the storage unit, wherein the storage unit stores, and the processing means is configured to execute, the instructions: connecting to a first base station, BS, and a second BS; communicating a first data with the first BS, wherein the first data is encrypted according to a first security key, which is generated according to a first parent key; communicating a second data with the second BS, wherein the second data is encrypted according to a second security key which is generated according to a second parent key; receiving a message from the first BS, wherein the message configures a handover to a third BS and a connection change to a fourth BS; connecting to a first base station, BS, and a second BS; communicating a first data with the first BS, wherein the first data is encrypted according to a first security key, which is generated according to a first parent key; communicating a second data with the second BS, wherein the second data is encrypted according to a second security key which is generated according to a second parent key; receiving a message from the first BS, wherein the message configures a handover to a third BS and a connection change to a fourth BS; updating the first parent key to a first updated parent key and updating the second parent key to a second updated parent key based on the first updated parent key in response to the message; updating the first security key to a first updated security key based on the first updated parent key and updating the second security key to a second updated security key based on the second updated parent key, in response to the message; communicating a third data with the third BS, wherein the third data is encrypted according to the first updated security key; and communicating a fourth data with the fourth BS, wherein the fourth data is encrypted according to the second updated security key.