ZnO as a wide band gap semiconductor is of significant interest for various applications, including dye-sensitized solar cell (DSSC) and photocatalytic degradation of organic pollutants. For DSSC, although the performance of ZnO-based devices is generally inferior to TiO2-based ones, it is still of interest due to its high electron mobility. While the relationship between the material and the device performance are complicated, many studies have been focused on morphologies and surface area of the nanomaterials. The studies of the effect of the material properties such as the types and concentrations of native defects on the DSSC performance have been scarce. For photocatalytic degradation of pollutants, many reports showed ZnO has a higher or similar efficiency compared to the commonly used TiO2. Reports have also pointed out the important role of native defects of ZnO in its photocatalytic activity. Nevertheless, the effect of the type and location of the defects has been contradictory in the literature indicating that there is a complex relationship. Therefore, we will discuss the effect of ZnO native defects on the dye adsorption, charge transport and hence the DSSC performance. We will also discuss their influence on reactive oxygen species (ROS) generation and photocatalytic dye degradation. As photoluminescence (PL) is a common methodology in studying native defects of ZnO, the relationship between PL, DSSC performance and photocatalytic properties will also be investigated. Preliminary results showed a higher overall PL intensity would result in a better device performance and higher photocatalytic activities.