Literature reveals that there are very few validated motor proficiency tests for young children. According to Gallahue and Ozmun, the Bruininks-Oseretsky Test of Motor Proficiency is a valid test. However, manipulative skills, which are classified as gross motor skills by most motor development specialists, are only tested in the Upper Limb Coordination Subtests but not in the Gross Motor Subtests of BOTMP. As there is no evidence that the five subtests of BOTMP: Running Speed and Agility, Balance, Bilateral Coordination, Strength and Upper Limb Coordination are of the same construct, this paper aims at using BOTMP to explore the construct validity of these five skills. The gross motor proficiency of 333 Hong Kong preschool children was assessed by the five subtests of BOTMP. The results indicated that the five subtests of BOTMP were of one underlying construct in measuring the gross motor proficiency of the preschoolers. (Contains 2 tables and 2 figures.)