A nanometer-scale post structure and a method for forming the same are disclosed. More particularly, a post structure, a light emitting device using the structure, and a method for forming the same, which is capable of forming a nanometer-scale post structure having a repetitive pattern by using an etching process, are disclosed. The method includes forming unit patterns on a substrate by use of a first material, growing a wet-etchable second material on the substrate formed with the unit patterns, and wet etching the substrate having the grown second material.