The original sample in this investigation included 36 children around the age of eight (mean age:8 year-lmonth) at the beginning. Study casts were obtained and measured every 6 months in two years of longitudinal study period in order to observe the changes of maxillary dental arch as well as the eruptional status of the maxillary lateral incisors. The results were as follows.: 1) The length of upper dental arch was increased gradually during the examination period. 2) The width between maxillary first molars was increased gradually during the examination period. 3) Intercanine distance in upper dental arch was increased gradually and the increment was conspicuous immediately after the eruption of maxillary lateral incisors.