A broadcast/communication convergence system and a method for transmitting and receiving Ethernet data using the same is disclosed. The system is equipped with an optical network unit performing a time division multiplexing operation on the Ethernet data switched by a network switch and a plurality of broadcast data units, transmitting a resultant signal of the operation to a corresponding subscriber set-top box, and providing data from the subscriber set-top box to the network switch. In one aspect of the invention, the optical network unit produces a length of an Ethernet data frame provided from the network switch. An encapsulation operation is carried out by generating data length information and inserting the generated length information into an Ethernet data frame. Encapsulated Ethernet data is transmitted to the subscriber set-top box. The subscriber set-top box carries out a time division demultiplexing operation for a signal transmitted from the optical network unit, and separates the signal into the Ethernet data and broadcast data. When a framing bit is detected from the frame of the Ethernet data based on a result of the separation, the length information is detected from the Ethernet data frame. The Ethernet data frame is counted on the basis of the detected length information and recognizing the Ethernet data. A preamble bit and a start-of-field delimiter (SFD) are inserted into the recognized Ethernet data and the original Ethernet data is recovered.