Provided is a method of and apparatus for compressing/decompressing data, in which lossless compression is applied to a raw data transfer mode in order to decompress data into high-quality data in a encoder/decoder (CODEC) system. A method of encoding data includes performing intraprediction within a current frame and performing interprediction between the current frame and a reference frame, applying lossless compression in input data in a raw data transfer mode in which raw data is transferred within an input frame, and comparing a predetermined parameter generated by the intraprediction and the interprediction with a predetermined parameter generated by the lossless compression, in order to select one of a prediction mode and a lossless compression mode.