Porous carbons with high surface area were successfully prepared from thermoplastic precursors, such as poly (vinyl alcohol) (PVA), by the carbonization of mixtures with MgO precursor at 900°C in inert atmosphere. MgO in the carbonization products was dissolved out by using a diluted acid, either sulfuric or acetic acid. The carbon precursors with MgO precursors (reagent grade magnesium acetate and citrate) were mixed either in powder (powder mixing) or in aqueous solution (solution mixing). Pore structure of the resultant carbons depended strongly on the mixing method. The BET surface area of the carbons obtained through solution mixing could reach to very high value, such as 2000 m2/g, even though any activation process was not applied. The carbons prepared through solution mixing method were rich in mesopores. By changing the size of MgO particles formed by pyrolysis of MgO precursor, the size of mosopores could be controlled. It was experimentally shown that substrate MgO was easily recycled.