[Purpose] To investigate the reliability and validity of the Alberta Infant Motor Scale (AIMS) in Japan, and to determine whether the AIMS score obtained by pediatric physical therapists with different levels of experience differed. [Subjects] The subjects who were assessed were 40 healthy infants (23 males, 17 females) whose parents gave their written consent to participation in this study. [Methods] 40 healthy children were videotaped and evaluated using the AIMS by three physical therapists who were providing physical therapy for the children on weekdays and three physical therapists who were providing physical therapy for the children once per week. The AIMS and the Kyoto Scale of Psychological Development (KSPD) were administered to confirm criterion-related validity. [Results] Reliability of the AIMS was good to high (ICC = .86∼.99), and the correlation between the AIMS and the KSPD was high (r = .97∼.98). Physical therapists with little experience in pediatric physical therapy could perform an assessment. [Conclusion] Both the reliability and the validity of the AIMS were high. Level of pediatric expertise did not affect a rater's reliability.