This paper reports the creation of a porous tin oxide structure by means of anodization of pure tin foil in alkaline NaOH solutions. The tin oxide film formed is polycrystalline and possesses an irregular nanoporous structure with a porosity of ∼50%. The average pore size is ∼37nm with a size distribution from 10 to 60nm irrespective of anodization conditions, including the applied voltage (5–15V) and NaOH concentration (0.125–1M). The BET specific surface area of this porous structure is 79.6m2/g. Linear relationships are observed for the dependence of tin oxide layer thickness on anodization time, applied voltage, and NaOH concentration. A thermodynamic model is established to explain the pore growth mechanism in the anodization process.