Provided is an apparatus and method for transmitting/receiving data in a communication system using a structured Low Density Parity Check (LDPC) code. The transmitter performs structured LDPC coding on input information data using a structured LDPC code, parallel-converts a structured LDPC codeword generated by performing the structured LDPC coding, in units of groups having a predetermined size, and transmits data. The receiver receives a plurality of parallel data streams, serial-converts the received parallel data streams in units of groups having a predetermined size, and performs structured LDPC decoding on the data which was serial-converted group by group, using a structured LDPC code.