Abstract: For the purpose of photocatalytic decomposition of organic dyes,the roller vibration milling was used to prepare ZnO nanostructures by two different ways:the one was to reduce directly the particle size of ZnO powders bought from the market to nanoscale in dry mode at room temperature,and the other was first to manufacture Zn quantum dots of 3-5 nm by the vibration milling under the same conditions,and then turned to ZnO particles by hydrolyzing Zn.The photocatalytic performance in degrading methyl orange in water was studied.For the commercial ZnO the optimal milling time leading to homogenous morphology and size distribution with mean diameter of 60 nm is 11 h,and the best catalyst dosage resulting in the highest decomposition of methyl orange is 50 mg.The decomposition degree reaches 97.91% when the ZnO nanostructures from the hydrolysis of Zn quantum dots are used,which is much better than that of the commercial counterpart.The possible reason might be that the former has morphology quite distinct from the latter,and possesses much better dispersivity under the same experimental conditions.