A method and apparatus for processing data in a Controller Area Network (CAN) are discussed. In an embodiment of this invention, dummy data is added to data to be transmitted via a CAN message, and information indicating that the dummy data is added is transmitted via the CAN message. A length of the dummy data is determined such that data to be transmitted via the CAN message becomes a predetermined length, and data in which five or more successive bits do not have a same value is added as the dummy data. The information is included in a field indicating a length of data to be transmitted via the CAN message, and is indicated by a value within a reserved range of the field. Accordingly, data processing efficiency can be improved, and flexible CAN communication can be performed via the CAN message.