Ten completely edentulous male patients; ranging in age from 45 to 50 years, were selected to study the effect of changing the vertical dimension of occlusion of complete denture wearers on the maximum biting force. For each patient five heat cured acrylic resin record blocks were constructed with different vertical dimensions. Bilateral seats in the premolar area were prepared within the occlusion rim to accommodate for the load cell used in biting measurement. The height of the load cell was 8 mm while the seats were prepared to be one mm less than the height of the load cell to facilitate the registration of the biting force. The base of the seat was prepared parallel to the occlusal plane. The biting force measurements were done by the record blocks with different vertical dimensions unilaterally (right side then left side measurements). The results of this study showed the values of biting forces upon changing the vertical dimension of occlusion in the right and left sides. When the vertical dimension of occlusion increased 3 mm there was an increase in the maximum biting force, while when the vertical dimension of occlusion increased 6 mm; the maximum biting force was decreased than that values obtained by 3 mm increase in vertical dimension. On the other hand when the vertical dimension of occlusion was decreased by 3 mm and 6 mm, the maximum biting force was decreased. The results of the present study concluded that the vertical dimension of occlusion is not an optimal vertical dimension that produces the maximum biting forces.