2D ordered, size-controlled nano-pillar was fabricated onto silicon substrate by direct nanosphere lithography with a mask of colloidal spheres. First, an ordered single layer of polystyrene (PS) nanosphere with a diameter of 200 nm was obtained by self-assembly on silicon surface. Then, the size of PS nanosphere on silicon substrate was reduced by reactive ion etching(RIE) with oxygen to form size-controllable PS nanosphere templates. Finally，these samples with nanosphere templates were etched by RIE with carbon fluoride to fabricate 2D ordered silicon pillar. The size of pillar is determined by the PS sphere diameter reducedby RIE and is controlled easily by choosing appropriate etching time. The period of silicon pillar arrays is determined by the initial diameter of PS spheres.