Purpose: In watching 3D stereoscopic display using the binocular disparity, effect of difference of the pupillary distance between the adults and children on the perception of depth were investigated. Methods: The average PD of children was determined from the PD measurements of children of the elementary school of 2nd and 3rd grade in Seoul. The location of crossing visual axes were derived from the relation of the binocular disparity and the PD for the adults and children. Results: The average PD of the children was measured to be 57.3 mm which was smaller than the average PD of the adults that was known to be about 65 mm. As the binocular disparity increases to the positive direction, the crossing location steeply moves farther behind the screen. On the other hand, when the binocular disparity increases to the negative direction, the crossing location gradually moves toward the viewer. For the same amount of the binocular disparity, the crossing locations were derived to be larger for the children than the adults due to the difference of the PD. Therefore, children will perceive larger depth than the adults. Conclusions: Small PD of the viewer causes the larger amount of the depth perception. In producing the stereoscopic images, the average PD of children as well as adults need to be considered.