The purpose of this study was to evaluate the reliability of the whole body reaction time as the motor ability measurements items for preschool children. The 221 boys and 210 girls of preschool children and 57 males performed five trials of the whole body reaction time. The preschool children were sorted 12 groups by age in every six months and sex. We calculated the relative value at median value of each subject. Each mean value of the minimum and maximum value from five trails of the male subjects were 0.308(92.7%) and 0.365(109.9%) seconds. In addition, every mean value for preschool children groups, the minimum value, the second value, the median value, the fourth value and the maximum value from five trials were 0.431-0.655(77.8-86.9%), 0.476-0.717(90.1-94.7%), 0.506-0.779(100%), 0.554-0.837(106.9-112.6%) and 0.622-0.943(118.1-132.3%) seconds. The mean value of the second and fourth relative values for preschool children groups were equivalent to the mean value of the minimum and maximum relative value for male subjects. The intra-class correlation coefficient of inter-trails (three data was excepted maximum and minimum value) for preschool children groups ranged of between 0.404 and 0.805. This mean value of preschool children correlated negatively with postnatal days (boys; r=-0.483 p<0.001. girls; r=-0.651 p<0.001). These results suggested the mean value of three data which was excepted maximum and minimum value in five trials was reliable as the motor ability measurements items for preschool children.