Background : Developmental and gender difference in motor ability among preschool-aged children were investigated by reference to performance of test items, based on measurement score. Purpose : The primary aim of this study was to verify development and gender difference in Innate Potential Motor Ability (IPMA), which is defined as non-differentiable ability, and the secondary aim was to explore the relationship between motor performance score and test item characteristics. Method : We tested 209 preschool children using 20 test items twice a year for two years, and derived mixed longitudinal data covering six periods during three years. Average standard scores were calculated for every term in order to derive estimates for the 20 items overall. The test items were assessed from the viewpoints of main functional organ, promptness of performance, formation of movement, physical fitness, and movement skills, and the relationships between these items and the average standard scores of motor performance were studied by multiple regression analysis using accumulated data representing dummy variables. In order to solve problems related to multicollinearity, principal components regression analysis was employed. Results and Discussion : The regression formula was shown to be predictive. IPMA for boys and girls, as represented by a partial correlation coefficient for every measurement item, was shown to develop with aging. There was no gender difference of IPMA among this cohort of preschool-aged children. The strongest relationship was evident between IPMA and motor performance score. Without IPMA, promptness of performance showed a relatively stronger relationship with motor performance score than the other characteristics of the test items. Internal promptness of performance, which demonstrates an individual's pace, was related to performance development. There was a weak relationship between elements of physical fitness and motor performance score.