The purpose of the study is to examine how an ordinal number concept is formed and what instructional procedure facilitates the acquisition of an ordlnal number concept. To study the former problem, the following 8 items are used: seriation, one to one correspondence, reversal correspondence, random correspondence, cardinal number and ordinal number (perceptual), cardinal number and ordinal number (random), number system (perceptual), number system (random). Seriation: Stimulus materials consist of ten cards which are the same width and the same length.Ss are instructed to form a staircase. with them.One to one correspondence: Stimulus materials are the same as those of seriation, and ten paper trees which are different lengths are used, too. These stimulus materials are the same as those of the following items.E arranges the two rows in correspondence one with the other.Then, E arranges the row of ten trees separately from. the row of the cards. E asks Ss on which step each tree is, pointing to the trees in the order 3, 1, 2, 6, 4, 5, 8, 10, 9, 7. Reversal correspondence: E arranges ten cards according to size and arranges ten trees in the reversal order. These trees are arranged separately from a staircase. E asks Ss on which step each tree is. Random correspondence: E arranges ten cards according to size and arranges ten trees regardless of size. E asks Ss on which step each tree is Cardinal number and ordinal number (perceptual): E arranges ten cards according to size like a staircase, and makes correspondence each step with each tree. Then, E covers steps with the flowers made of paper. A staircase is covered with the flowers, so Ss can not see the steps. E tells Ss that each step was made by piling up the stones one by one. E asks Ss how many stones each step consists of. Cardinal number and ordinal number (random): The same materials and procedures as those of cardinal number and ordinal number (perceptual) are used. Each stimulus material is arranged in random order. Number system (perceptual): The same materials as those of cardinal number and ordinal number (perceptual) are used. E asks Ss,“How many steps have you climbed when you are at this step?” pointing to each tree. Then, E asks Ss,“How many steps remain to be climbed, when you are at this step?” Number system (random) The same materials as those of cardinal number and ordinal number (random) are used. Ss are asked to answer the same questions as those of number system (perceptual). To study the latter problem, three experimental groups and one control group are used. Ss are 60 5-year-old children. Each group consists of 15 members. E instructs the first experimental group in the verbal label, the second experimental group in number system, and the third experimental group in the verbal label and number system. Each experimental manupulation is introduced between two tests. The results are as follows: To solve the former, problem, the before test is analysed. The percentages of correct respondents to items are as follows. Number system (random)(5%), random correspondence (10%), cardinal number and ordinal number (random)(12%), cardinal number and ordinal number (perceptual)(28%), number system (perceptual)(32%), reversal correspondence (48%), one to one correspondence (80%), seriation (98%). The index of reproducibility is, 93.These items are scalable. To solve the latter problem, both before and after tests are analyzed. There are no significant differences among the experimental groups. There is a significant difference between each experimental group.and the control group. The third experimental group shows an effect of experimental manipulation on cardinal number and ordinal number (random).This means that the experimental manipulation to relate theverbal label to the nmber system makes an effect on Ss. The second experimental group shows no effect of an experimental manipulation on number system.