This paper is devoted to the decontamination of wastewater using ZnO nanostructures. The photocatalytic degradation of aqueous solution of a commercial dye, toluidine blue (TBO), has been investigated with two different kinds of ZnO nanostructures comprising butterfly-type ZnO nanorods and randomly-oriented ZnO nanorods. In order to be able to compare the photocatalytic efficiency, ZnO photocatalysts with two different crystalline structures are prepared by using different precursors but operating same microwave-assisted method. Butterfly-type ZnO nanorods are synthesized by using surfactants. Randomly-oriented ZnO nanorods with environmentally-friendly method are obtained without using any base and surfactant. The two different kinds of ZnO photocatalysts are characterized by X-Ray diffraction (XRD), scanning electron microscopy (SEM), UV-Vis absorption spectrum. The effects of pH, ZnO catalyst dosage and TBO initial dye concentration are tested experimentally for photocatalytic degradation.. After 90 minutes reaction time, the decolorization efficiency of the TBO achieved 85.20% for butterfly-type ZnO nanorods and 77.20% for randomly-oriented ZnO nanorods. Additionally, under the same optimum conditions of pH=11, [ZnO]= 1g-ZnO L-1 [TBO]= 108 mg TBO L-1, Total Organic Carbon (TOC) removal efficiencies are obtained 56.70% and 40.80% for butterfly-type ZnO nanorods and randomly-oriented ZnO nanorods, respectively.