Individuals with intellectual disabilities show observable delays in motor development. It is believed that children with mild intellectual disabilities are 2 to 4 years behind normal peers on measures of motor performance. However, this belief requires further evaluation for adolescents with mild intellectual disabilities because the number of delayed years in motor development seems to be increased following the number of chronological ages by this population. The purpose of this investigation was to examine the number of delayed motor developmental years by adolescents with intellectual disabilities. Participants were 12 adolescents, diagnosed with mild intellectual disabilities based on school files, 6 males and 6 females, ages from 12 to 15 years old, from an adapted PE class in a school. They were measured using Bruininks-Oseretsky Test of Motor Proficiency by a trained person, a graduate student in the master?s degree adapted physical education program. Averaged point score on each of the 8 subtests was calculated first and the resulted mean score was then employed to determine the age equivalent of this subtest area based on the Norm of Age Equivalents Corresponding to Subtest Point Scores provided in Bruininks-Oseretsky Test of Motor Proficiency Manual. The number of delayed years in motor development on each subtest area was computed by subtracting the age equivalent found in the Norm from the averaged chronological age. Results of this study revealed that adolescents with mild intellectual disabilities delayed in 9 years and 3 months in running speed and agility, 8 years and 9 months in balance, 7 years and 9 months in bilateral coordination, 5 years and 6 months in strength, 6 years and 6 months in upper-limb coordination, 9 years and 10 months in response speed, 7 years and 6 months in visual-motor control, and 7 years and 9 months in upper-limb speed and dexterity. These results indicate that adolescents with mild intellectual disabilities are 6 to 10 years behind their normal peers on measures of motor performance, rather than 2 to 4 years behind their normal peers on measures of motor performance shown by children with mild intellectual disabilities, supporting that the number of delayed years in motor development increases following the number of chronological ages by individuals with intellectual disabilities. It is recommended, however, that result of this investigation be replicated and extended in future studies due to that the sample of this study was relatively small. Keyword(s): research