This study develops and validates a halal tourism service quality scale using data from 520 Muslim travellers visiting island destinations in Malaysia, Thailand and Vietnam. Halal tourism has grown into a substantial segment of Southeast Asian travel, yet destinations differ widely in the extent to which they accommodate the religious requirements of Muslim visitors, and existing service quality instruments do not capture the attributes that matter most to this market. Following established scale development procedures, an initial pool of 38 items was generated from the literature, interviews with 22 travellers and expert review, and refined through a pilot study. The main survey was administered at Langkawi, Phuket and Phu Quoc, and the sample was split for exploratory and confirmatory factor analysis. The final 24-item scale comprises six dimensions: prayer facilities, food assurance, staff awareness, accommodation privacy, destination environment and information accessibility. All dimensions demonstrated satisfactory reliability and convergent and discriminant validity, and the measurement model was invariant across the three destinations. Structural analysis showed that prayer facilities, food assurance and staff awareness are the dimensions most strongly associated with loyalty, measured as intention to revisit and to recommend, with satisfaction partially mediating these relationships. Accommodation privacy and information accessibility had smaller effects, and destination environment was not significant once other dimensions were controlled. The scale offers destination managers a diagnostic tool for prioritising investment in halal-friendly services, and the findings suggest that the most influential attributes are those that affect daily religious practice during the visit.