Introduction: The Sport Motivation Scale-II (SMS-II) has been widely employed to assess motivational orientations in athletic populations; however, its measurement properties remain subject to debate. This systematic review aimed to evaluate the measurement properties of SMS-II and synthesize the quality of evidence using the COnsensus-based Standards for the selection of health Measurement INstruments (COSMIN) methodology. Methods: A comprehensive literature search of PubMed, Web of Science, EMBASE, PsycInfo, and CINAHL databases was conducted up to 20 March 2026 to identify studies reporting psychometric evaluations of SMS-II. Measurement properties were appraised against the COSMIN quality criteria, while methodological rigor was assessed using the COSMIN risk-of-bias checklist. Results: Moderate-quality evidence supported the sufficiency of content validity (relevance and comprehensibility) and six-factor structural validity (supported by 76.5% of included studies). Furthermore, high-quality evidence from a subset of studies (two studies) supported sufficient five-factor structural validity. High-quality evidence also supported sufficient cross-cultural validity and measurement invariance, internal consistency for the six-factor structure (Identified subscale) and five-factor structure (Integrated and Intrinsic subscales), test-retest reliability (except for the Identified subscale), and hypothesis testing for construct validity. Conversely, two-, three-, and four-factor structural validity solutions, as well as internal consistency for the Identified, External, and Amotivated subscales within the five-factor structure, were rated as insufficient. The remaining measurement properties demonstrated inconsistent findings despite high-quality evidence. Discussion: While specific structural models (two-, three-, and four-factor) and the internal consistency of certain subscales within the five-factor model received insufficient ratings, the core measurement property of the SMS-II as a whole was classified as inconsistent. These findings indicate that the SMS-II can be cautiously utilized, although additional high-quality research is required to establish the sufficiency of its currently inconsistent measurement properties. Systematic review registration: https://www.crd.york.ac.uk/PROSPERO/view/CRD420251163217, CRD420251163217.
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