Natural zeolite rock of which dominent clay minerals were mordenite and clincptilolite was collected from Wolsung, Kyungpook province. It was pulverized and sieved into four fractions of 1∼0.5, 0,5∼0.25, 0.25∼0.1, and $lt;0.l㎜. The specific surface areas of its four fractions were determined by H₂O and EGME. The specific surface area of zeolite was slightly affected according to species of measuring material, but was scarcely affected by partical size, nor increased of pulverizing. The surface area of zeolite was calculated from geometric structure of mordenite and it was compared with the specific surface area calculated from maximum numbers of H₂O which could be adsorbed on mordenite. On the basis of that result, the specific area measured from zeolite was estimated to be a part of surface area calculated from it. Accordingly, it was suggested ti at a new method should be developed for the determination cf an exact surface area of zeolite.