A method of overwriting data in a write-once information storage medium and a data recording and/or reproducing apparatus therefor. In the data overwriting method, a command to overwrite new data in a first area of the write-once information storage medium where data has already been recorded is issued. Then, the first area is considered as a defective area, and the new data is recorded in a second area. Thereafter, updated defect management information, including information about the locations of the first and second areas, is recorded in the write-once information storage medium. Accordingly, overwriting can be performed in write-once information storage media, which is incapable of physical overwriting, by using a logical overwriting technique. Thus, data recorded in the write-once information storage medium may be changed or updated.