The purpose of this study was to investigate bias in motor ability and to examine the relationship between bias and lifestyle in preschool-aged children. Twentyone motor ability test (MAT) items were administered to 1,409 children. A questionnaire survey on the children's lifestyles was also completed by the parents. A factor analysis on the MAT test items revealed the following factors: “ locomotive movement when jumping (LJ),” “ ability of running (AR),” “ rhythm (RM)” and “ manipulative movement (MM).” In relation to each of these factors, children were ranked as “good,” “average” or “poor” and the following two patterns relating to bias in motor ability in young children observed: poor AR and RM with good LJ and MM, and vice versa. Through logistic regression analysis, a relationship between bias in motor ability and lifestyle was found in (i) children with no older sibling, (ii) those playing in open areas such as outdoors or on school playing grounds, and (iii) those children not motor playing after preschool. The seasonal change in the bias resulted in the following children ― those with no siblings, those not learning sports, those with their own private rooms―either shifting from “good in LJ and MM” to “good in AR and RM” or shifting from non-bias to bias. The study showed that the time, area and peers for play related to be factors not only a decline in physical fitness, but also the bias in motor ability.