ZnO nanorods were prepared through a sol-gel process by adding various amounts of water at low temperature and atmospheric pressure conditions for application as a photocatalyst. The 1-D ZnO nanostructures can overcome fast recombination of photogenerated electrons and holes that inhibits photocatalytic efficiency. X-ray diffractometer and transmission electron microscopy measurements confirmed that the (002)/(100) intensity ratio increased from 0.83 to 1.34 and the morphology of the ZnO nanoparticles was changed from a spherical shape to nanorods with the addition of water. UV-vis spectroscopy showed a red shift from 360 nm to 371 nm, which indicates a decrease of the band gap energy. PL measurements of the ZnO nanorods showed a 103 times improvement of the NBE/DLE intensity ratio compared to the ZnO nanospheres. When the photocatalytic efficiency of the ZnO nanoparticles was estimated for the degradation of methylene blue dye under irradiation of UV light, the photocatalytic kinetic constant increased from 0.067 min-1 to 0.481min-1. As a result, longer ZnO nanorods showed better photocatalytic performance.