ZnO particles were synthesized by a parallel flow precipitation hydrothermal process with Zn(NO3)(2)center dot 6H(2)O and NH3 center dot H2O as raw materials. The morphology and structure of as-synthesized ZnO particles were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and Brunauer-Emmett-Teller (BET) surface area analysis. The results revealed that all of the obtained ZnO samples had a hexagonal wurtzite structure, with the precipitation reaction pH being a key factor in the formation of the hexagonal prism structure. The photocatalytic activity of ZnO was evaluated via Rhodamine B (RhB) dye degradation. The ZnO-3 sample synthesized at a precipitation pH = 6.8 possessed excellent photocatalytic degradation effciency after three photocatalytic experiments. No significant change of photocatalytic activity could be detected when NO3- was added, however, the presence of SO42- and Cl- reduced the photocatalytic activity, with SO42- most severely reducing activity.