Thick anodic layers on pure Mg were produced by anodization in a nonaqueous electrolyte. The most promising systems for growth of thick, uniform anodic layers were nominally water-free methanol or ethanol electrolytes containing nitrate ions. The layer thickness shows a linear dependence on the applied voltage and on the anodization time. This nonlimited layer growth, leading to a very high thickness with time (e.g., up to 30 mu m with 30 min at 20 V for the methanol system), suggests a porous nature of the layer. Scanning electron microscopy examination of the surface morphology indeed reveals nanopores/flakes in the layer. In addition, the porosity of the layer can be tuned by the use of ethanol and methanol mixtures as an anodization bath. The chemical composition of the films was examined by using X-ray photoelectron spectroscopy and energy-dispersive X-ray analysis, which reveals that the anodic layer consists of mainly Mg, O, and C (without toxic or environmentally hazardous species). Furthermore, the layers can be converted into crystalline MgO upon annealing without significant loss in morphology. This type of thick nanoporous layer is a promising candidate for the functionalization of Mg surfaces for different applications.