The aim of this study was to investigate dentinal tubule diameter and dentinal tubule density in primary teeth and to compare those values between each tooth type at electron microscope level. Thirty freshly extracted primary teeth were included in this experiment and categorized into six groups according to their tooth types and dental arches. All samples were first sectioned longitudinally, and then sectioned perpendicular to the direction of dentinal tubules which directed from the pulpal horn at three levels represented outer, middle and inner dentin. The result revealed that the diameter and density of dentinal tubule increased from outer dentin toward the pulp. The mean±SD of tubule diameter was largest in maxillary molar (1.44±0.24μm) and smallest in mandibular incisor (1.15±0.18μm). The density of dentinal tubules was greatest in mandibular incisor (58,080.33 tubules/mm2) and lowest in maxillary molar (27,476.26 tubules/mm2). The diameter of dentinal tubules tended to increase from anterior to posterior teeth, while, conversely, tubule density decreased from anterior to posterior teeth.