Tin dioxide (SnO 2 ) is an important material in the field of solid-state gas sensors and the performances are strongly linked to the microstructure. Particularly, a decrease in the crystallite grain size leads to an increase in the sensing properties. Many chemical and physical techniques have been used to prepare nanosized SnO 2 particles, but few papers report the use of a ball-milling process that promote nanostructured grains. In this work, tetragonal phase SnO 2 powders were produced at room temperature (RT) by reactive milling of metallic tin (Sn) powder under pure oxygen atmosphere in a vertical planetary ball-mill. Powder samples were characterized by using X-ray diffraction (XRD), secondary electron microscopy (SEM), electron microprobe. Experimental results indicate that the formation of SnO 2 is a mechanically induced self-sustained reaction. Very short milling time is needed to complete the reaction and the obtained powder is made of aggregates of SnO 2 crystallites, the mean size of which is inferior to 10 nm according to XRD analyses. However, the strong agglomeration led to a decrease of the specific surface area. The reasons and the possible ways to overcome these phenomena are discussed.