Provided are a porous composite expressed by Chemical Formula 1 and having a porosity of 5% to 90%, and a method of preparing the same: MOx   where M and x are the same as described in the specification. According to the present invention, since a molar ratio (x) of oxygen to a molar ratio of (semi) metal in the porous composite is controlled, an initial efficiency of a secondary battery may be increased. Also, since the porous composite satisfies the above porosity, a thickness change rate of an electrode generated during charge and discharge of the secondary battery may be decreased and lifetime characteristics may be improved.