My thesis target was design an Ethernet dual UART Converter, wich can create two-way communication between the Ethernet network and the serial lines. During my literature search I collected the TCP/IP protocols (DHCP, TCP, UDP, ARP, HTTP), that the device needs for network communication. For planning the hardware and the software I examined the Ethernet serial converters, that are available on the market. I choose the prototype’s microcontroler based on the hardware parameters of the Ethernet converters, that I've found on the market. Since the devices support multiply standards, I add RS422, RS485 and LVDS transceivers circuits to the prototype. I accomplished the prototype with existing development boards. The microcontroler's software is written in language C. For the implementation of the network communication I used lwIP TCP/IP stack. Besides the data sendings, the user can configurate the serial ports settings via network and he will also be certified about the events from the serial ports, that are provided with timestamps. For the portability of the programcode I tried to make the code as independent from the hardware as possible. Furthermore, I minimized the numbers of data movement in the software, and the remained copies are done by the microcontrollers DMA. For testing the prototype, I created a (PC client program), that is able to send and receive datas from the device by using TCP protocol.