: This paper designs and implements an industrial internet of things (IIoT) platform based on manufacturing message specification (MMS) with enhanced security through unidirectional data transmission. Unidirectional gateways are used to overcome transferring between separated industrial networks based upon UDP(User Datagram Protocol) and are capable of transferring information between networks. However, additional gateways are required for network connectivity. The proposed platform supports unidirectional communication between networks using a message queue telemetry transport (MQTT) broker, which acts as a gateway in unidirectional communication. In addition, MMS over MQTT protocol (MoM) is designed using publishing and subscription functions of MQTT. In order to evaluate the performance of the proposed platform, we compared it against the performance of the UDP used in the existing unidirectional gateway. Simulation results demonstrate that the proposed platform has a slower transmission time than UDP, but the reliability of data transmission is higher when a large number of packets are transmitted to one port.