A method for transforming data to reduce an amount of data in a communication system equipped with several sub-carriers, and a data transmission method using the same are disclosed. The method for transmitting data using a Discrete Cosine Transform (DCT) in a communication system based on a plurality of sub-carriers includes: a) performing a Discrete Cosine Transform (DCT) on first data; b) selecting a predetermined number of data from among the DCT-processed first data, and performing data processing on the selected data; and c) transmitting the data-processed resultant data to a reception end. A method for reducing an amount of overhead of transmission data for use in the multi-antenna communication system is disclosed.