Previously, we reported the magnetic nanowires army can be used to separate magnetic nanoparticles from the colloidal suspension.The mechanism lies in the high aspect ratio of nanowire.Here, it is showed that the nanowires array can also be used to improve the dispersivity of magnetic nanoparticles.We had the colloidal suspension flow through the magnetic nanowires array, collecting the fluid in the drain end.It was found by SEM that the relatively larger particles were trapped on the nanowires array and the size distribution was narrowed.