Conductive-atomic force microscopy has been successfully used for characterizing recorded marks on commercial digital versatile disk and Blu-ray disk. Nano recorded marks beyond diffraction limit are imaged with high spatial resolution and excellent contrast of conductivity. The smallest mark size resolved is around 23.5 nm which is limited by background spots around 18.5 nm. The results of different optical power and writing strategy on the size, shape, and close packed writing process of recorded marks clearly show the opto-thermal response of phase-change recording layer.