The present invention relates to a plastic substrate having a multi-layer structure and a method for preparing the same. The plastic substrate of the present invention comprises plastic films attached to each other, and a first buffering layer of an organic-inorganic hybrid, a layer of gas barrier, and a second buffering layer of an organic-inorganic hybrid which are stacked on both sides of the plastic films in an orderly manner, each layer forming a symmetrical arrangement centering around the plastic films.Because the plastic substrate of the present invention has a small coefficient of thermal expansion, excellent dimensional stability, and superior gas barrier properties, it can replace the brittle and heavy glass substrate in display devices. Also, it can be used for a variety of packaging or container materials in applications requiring superior gas barrier properties.