Fascicle arrays of gallium nitride (GaN) nanostructures were grown on silicon nanoporous pillar array (Si-NPA) by a reactive chemical vapor deposition method. Through adjusting the distance between the gallium source and Si-NPA substrate, the morphology of GaN nanostructures was tuned from cone-strings, cone-strings plus nanowires to nanowires, accompanied with the average diameter changed from similar to 800 nm to similar to 13 nm. Both the cone-strings and the nanowires were found growing along [0001] direction. These results indicate that Ga concentration is a key factor in determining both the morphology and the average diameter of GaN nanostructures. The growing process of the GaN nanostructures was explained under the frame of vapor-liquid-solid deposition mechanism. Our method might be expanded to the growth of other compound semiconductor nanostructures on patterned silicon substrates for constructing functional nanodevices. (C) 2012 Elsevier B.V. All rights reserved.