Recently, photodetector such as wearable optical sensor or portable photoconductive devices have been widely studied. And as global warming accelerates, the rate of harmful ultraviolet rays entering the earth is increasing, so photodetector research is underway to prevent diseases caused by ultraviolet rays. For the fabrication of flexible photodetector, hydrothermal methods which can grow at low temperature was introduced by using PES substrate. In order to grow Mg-doped ZnO (MZO) nanorods on amorphous plastic substrates, ZnO and MgZnO seed layer were deposited by a sputtering system and the characteristics of seed layer were analyzed according to the type of seed layer. ZnO nanorods were doped with Mg(NO3)2 and (CH3COO)2Mg precursor to dope Magnesium. And the precursor species and doping concentration were analyzed. We fabricated a flexible photodetector using MZO nanorods according to the growth time and analyzed structural, optical-electrical characteristics. The structural characteristics of the MZO nanorods grown on the ZnO seed layer were superior to those of the MgZnO seed layer. The structural and electrical properties of the MZO nanorods doped by Mg(NO3)2 precursors were excellent. The nanorods doped at 3 at.% using the Mg(NO3)2 precursor on the ZnO seed layer had the best electrical properties and are considered to be applicable to photodetectors. MZO nanorods photodetectors fabricated using Mg(NO3)2 precursors on the ZnO seed layer are most stable when grown for 2 hours. It is expected that a photodetector of better quality can be obtained by future electrode structure and process optimization.