A remote diagnostic system (RDS) data security device and method are provided, in which an interface unit receives an RDS command from a host, a storage unit stores a security setting for RDS data, and a control unit performs an operation for the RDS data according to the RDS command and the security setting, wherein the result obtained by the performance is selectively transmitted externally. Accordingly, since the reading and writing operations of RDS data are performed according to an RDS command received from the host and previously stored security setting, and the result obtained by the reading and writing operations is displayed, data collected in the RDS can be prevented from being transmitted to the server without permission, and data allowed to an authorized user can be transmitted to the server.