Provided are a substrate supporting unit and an apparatus and method for polishing a substrate using the same. The substrate supporting unit vacuum-absorbs a bottom surface of the substrate during a polishing process, and supports the substrate in a state where the substrate is upwardly spaced from the substrate supporting unit to clean the substrate during a post-cleaning process. Therefore, in the substrate supporting unit and the apparatus and method for polishing the substrate using the same, a polishing process on a top surface of the substrate and a post-cleaning process on the top and bottom surfaces of the substrate may be sequentially performed in a state where the substrate is supported by a single wafer type substrate supporting unit.