Several chemical methods were introduced for synthesis zinc oxide (ZnO) nanoparticle (NP). The morphology of the obtained powder varied based on process parameters, which can affect final properties of powder. In this study, ZnO-NP synthesized via hydrothermal technique using zinc nitrate hexahydrate (0.1 and 1.0 M) and urea (0.2 and 2.0 M). Moreover, different synthesis times (3 and 5 h) and temperatures (130 and 150 °C) were used. The X-ray patterns of ZnO-NP demonstrated ZnO peaks without the presence of any impurities. Furthermore, surface analysis results indicated the only presence of elemental peaks for Zn and O. The morphology analysis illustrated distinct microstructures, including unique multi hollow flakes, with a crystal size from 18.80 to 23.60 nm. The voids on the flake-like structure were in the range of 10 to 54 nm. The thermal and optical properties and photodegradation performance of synthesized ZnO-NP against organic dyes were also studied.