The Alberta Infant Motor Scale (AIMS) is a widely used screening tool used to measure gross-motor maturation for clinical and research usage in various countries. A cross-cultural translation and adaptation process is essential to produce reliable and applicable translated assessment tools.The purposes of this cross-sectional study were to obtain the Alberta Infant Motor Scale Thai version and to determine its reliability, validity, and applicability.The process of translation and cultural adaptation of the AIMS Thai version was performed. The conceptual, semantic, and idiomatic equivalences of the language of the AIMS Thai version were strictly reviewed by committee. The intra-rater/inter-rater reliabilities and concurrent validity with the Bayley III were examined in 30 full-term typically developing infants. Then, 19 infants from an orphanage and 23 typically developing infants were assessed using the final translated version of the AIMS.The AIMS Thai version was generated systematically. Two therapists showed high intra-rater reliability using the Thai AIMS with an ICC of 0.995 (95% CI 0.989-0.998) and 0.979 (95%CI 0.919-0.992), and the inter-rater reliability was 0.988 (95%CI 0.976-0.994). The concurrent validity of the AIMS Thai version and the Bayley III was 0.969 (p < 0.01). The AIMS percentile of gross-motor development of orphaned infants (94.7%) were equal or lower than the 5th percentile, while the AIMS percentile of home-raised infants ranged from the 5th to the 90th percentile.The translated and adapted AIMS Thai version is reliable and valid to use in Thai infants.