SiO(2) hierarchical nanostructures consisting of a wire-like main stem and lots of rod-like sub-branches have been synthesized by a magnesium catalyzed thermal evaporation process. It is indicated that magnesium plays a critical role in the synthesis of SiO(2) hierarchical nanostructures including promotion for SiO evaporation and hierarchical-like growth of SiO(2). Moreover, the photoluminescence (PL) analysis of the SiO(2) hierarchical nanostructures reveals that blue and ultraviolet (UV) emissions are detected, which are different from those of other SiO(2) nanostructures. Finally, the growth mechanism and PL emission of SiO(2) hierarchical nanostructures have been preliminarily discussed.