A method of preparing purified decitabine comprises mixing crude decitabine with solvent, such as dimethylacetamide, to form a solution or suspension and forming the purified decitabine from the solution or suspension. The forming step comprises adding an anti-solvent, such as ethanol, to the solution or suspension. The forming step may further comprise after adding ethanol to provide a mixture of dimethylacetamide and ethanol: cooling the mixture; isolating the solid decitabine present in the cooled mixture; and evaporating residual dimethylacetamide and ethanol from the solid decitabine to provide the purified decitabine. The mixture of dimethylacetamide and ethanol may be heated. The purification method preferably results in decitabine having a ratio of the β-anomer of decitabine to the α-anomer of decitabine of at least about 99.9:0.1.