The present invention relates to a microcellular foam of a thermoplastic resin and a method for preparing the same, and more particularly to a microcellular foam comprising a skin layer having a porosity of below 5% and a core layer having a porosity of at least 5%, wherein the thickness of the skin layer accounts for 5 to 50% of the entire foam, and a method for preparing the same. The microcellular foam of the present invention is advantageous in that it has a thicker skin layer and smaller and uniform micropores in the core layer, compared with conventional microcellular foams, while having mechanical properties comparable to those of conventional non-foamed sheets.