Provided are a recording/reproducing apparatus and method for optimizing data recording. The recording/reproducing apparatus sets a predetermined length which is an integer multiple of a unit recording length and sets a plurality of recording parameters, with reference to mark/space combinations which can be configured within the predetermined length ahead of a start point of a mark for recording data and mark/space combinations which can be configured within the predetermined length behind an end point of the mark for recording data. Accordingly, by setting a predetermined length and limiting conditions for optimizing recording parameters, and considering run-length combinations which can be configured within the predetermined length, it is possible to quickly and efficiently optimize parameters.